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Friday, 31 August 2018

Function of liver in digestive system




What is the liver? Describes the function of liver in digestion.


The liver, the largest organ in the mammalian body, that lies just under the diaphragm.
In the liver, millions of cells that is called hepatocytes take up nutrients that absorbed from the intestines and release them into the bloodstream. Hepatocytes perform the function the manufacture of blood proteins prothrombin and albumin.

Some major metabolic functions of the liver are given below:

1. Removal of amino acids from organic compounds.
2. Urea formation from proteins and conversion of excess amino acids into urea to decrease body levels of ammonia.
3. Manufacture of most of the plasma proteins, formation of fetal erythrocytes, destruction of worn-out erythrocytes, and synthesis of the blood-clotting agents prothrombin and fibrinogen from amino acids.
4. Synthesis of nonessential amino acids.
5. Conversion of galactose and fructose to glucose.
6. Oxidation of fatty acids.
7. Formation of lipoproteins, cholesterol, and phospholipids.
8. Conversion of carbohydrates and proteins into fat.
9. Modification of waste products, toxic drugs, and poisons.
10. Synthesis of vitamin A from carotene, and with the kidneys,
participation in the activation of vitamin D.
11. Maintenance of a stable body temperature by raising the temperature of the blood passing through it. Its many metabolic activities make the liver the major heat producer in a mammal’s body.
12. Manufacture of bile salts, which are used in the small intestine for the emulsification and absorption of simple fats, cholesterol, phospholipids, and lipoproteins.
13. Main storage center. The liver stores glucose in the form of glycogen, and with the help of insulin and enzymes, converts glycogen back into glucose as the body needs it.

 The liver also stores fat-soluble vitamins (A, D, E, and K), and minerals, such as iron, from the diet. The liver can also store fats and amino acids, and convert them into usable glucose as required.


Function of Pancreas in Digestive System




Function of the Pancreas In Digestion


The pancreas is an organ that lies ventral to the stomach and consist of both endocrine and exocrine functions.

 The function exocrine cells in the pancreas secrete digestive enzymes into the pancreatic duct, which unite with the hepatic duct from the liver to form a common bile duct that enters the duodenum. Pancreatic enzymes complete the digestion of carbohydrates and proteins and initiate the digestion of lipids. Trypsin, carboxypeptidase, and chymotrypsin digest proteins into small peptides and individual amino acids.

 Pancreatic lipases split triglycerides into smaller, absorbable glycerol and free fatty acids. Pancreatic amylase converts polysaccharides into disaccharides and monosaccharides.

The pancreas also secretes bicarbonate (HCO3) ions that help neutralize the acidic food residue coming from the stomach. Bicarbonate raises the pH from 2 to 7 for optimal digestion. Without such neutralization, pancreatic enzymes could not
function.

large intestine function in digestive system




Function of large intestine in digestion


The large intestine lack circular folds, villi, or microvilli and has the much smaller surface area. 

The small intestine joins the large intestine near a blind-ended sac, that is called
cecum.  The human cecum and its extension, the appendix, are storage sites and possibly represent evolutionary remains of a larger, functional cecum, such as is found in herbivores.

The appendix consist of greater number of lymphoid tissue and perform the function of immune system. The major functions of the large intestine contain the
reabsorption of water and minerals, and the formation and storage of feces. As peristaltic waves move food residue along, minerals diffuse or are actively transported from the residue across the epithelial surface of the large intestine into the bloodstream.

 Water follows osmotically and returns to the lymphatic system and bloodstream. When water reabsorption is insufficient, diarrhea results.
 If too much water is reabsorbed, fecal matter becomes too thick, resulting in
constipation.

Many bacteria and fungi exist symbiotically in the large intestine. They feed on the food residue and further break down its organic molecules to waste products. Then they secrete amino acids and vitamin K, which the host’s gut absorbs. But
remains
feces is a mixture of bacteria, fungi, undigested plant fiber, sloughed-off intestinal cells, and other waste products.


Sunday, 26 August 2018

Role of small intestine in Digestion




Role of small intestine in Digestion


Small intestine is the main site of digestion in which most ingested food of mammals is digested and absorbed in the small intestine.

Size of small intestine
The size human small intestine is about 4 cm in diameter and 7 to 8 m in length  It is intermediate in length between the small intestines of typical carnivores and  small intestine of herbivores of similar size, and it reflects the human’s omnivorous eating habits.
 The length of the small intestine directly relates to the total surface area available for absorbing nutrients, as determined by the many circular folds and minute projections of the inner gut surface (figure a). On the circular folds, thousands of fingerlike projections called villi. Villi  project from each square centimeter of mucosa (figure b).

Columnar epithelial cells, contain numerous microvilli, cover both the circular folds and villi (figure
c). These small projections are so dense that the inner wall of the human small intestine has a total surface area of approximately
300 m2
the size of a tennis court.


Part of small intestine
Duodenum
The first part of the small intestine, called the duodenum, functions primarily in digestion. The duodenum consist of many digestive enzymes that intestinal glands in the duodenal mucosa secrete. The pancreas secretes other enzymes. In the duodenum, digestion of carbohydrates and proteins is completed, and most lipids are digested.

Jejunum or Ileum
 The next part is the jejunum, and the last part is the ileum. Both function in nutrient absorption. The jejunum and ileum absorb the end products of digestion such as, amino acids, simple sugars, fatty acids, glycerol, nucleotides, water.
Much of this absorption involves active transport and the sodium dependent ATPase pump.

 Sugars and amino acids are absorbed into the capillaries of the villi, whereas free fatty acids enter the epithelial cells of the villi and recombine with glycerol to form triglycerides. The triglycerides are coated with proteins to form
small droplets called
chylomicrons, which enter the lacteals of the villi.

 From the lacteals, the chylomicrons move into the lymphatics and eventually into the bloodstream for transport throughout the body. Besides absorbing organic molecules, the small intestine absorbs water and dissolved mineral ions. The small intestine absorbs about 9 liters of water per day, and the large intestine absorbs the rest.

Role of stomach in mammalian digestion



Role of stomach in mammalian digestion


The mammalian stomach is a muscular, distensible sac that contain three
main functions.
(1) It stores and mixes the food bolus that received
from the esophagus.
 (2) Secretes substances such as enzymes, mucus, and hydrochloric acid [HCl] that digest the protein.
(3) Stomach also helps to control the rate at which food moves into the small
intestine through the pyloric sphincter (figure
a).
The stomach is made up of an inner mucous membrane containing thousands of gastric glands (figure
b).

Types of gastric glands

 
Parietal cells that secrete a solution that contain HCl.
 Chief cells that secrete pepsinogen, the make from the enzyme pepsin. Both of the cells are in the pits of the gastric glands.
Mucous cells
The surface of the mucous membrane at the openings of the glands contains numerous
mucous cells that secrete mucus that cover the surface of the stomach and protects it from the HCl and digestive enzymes.

Function of some hormone in stomach

 The surfaces of the upper gastrointestinal tract the esophagus and mouth have a much thinner mucous-cell layethan the stomach, which is why vomiting can cause a burning sensation in the esophagus or mouth. Endocrine cells in one part of the stomach mucosa release the hormone gastrin, which travels to target cells in the gastric glands, further stimulating them.

When the bolus of food enters the stomach, it distends the walls of the stomach. This distention, as well as the act of eating, causes the gastric pits to secrete HCl and pepsinogen. The H
ions cause pepsinogen to be converted into the active enzyme pepsin. As pepsin, mucus, and HCl mix with and begin to break down proteins, smooth mucosal muscles contract and vigorously churn and mix the food bolus.

 About three to four hours after a meal, the stomach contents have been sufficiently mixed and are a semiliquid mass called chyme .The pyloric sphincter regulates the release of the chyme into the small intestine.

Sensation of hunger pangs
When the stomach is empty, peristaltic waves cease, after about 10 hours of fasting, new waves  comes from the upper region of the stomach. These waves can cause hunger pangs as sensory nerve fibers carry impulses to the brain.

Role of Oral cavity in Mammalian Digestion




Role of Oral cavity in Mammalian Digestion

 Oral cavity is protected by the pair of lips. The lips consist of vascularized, skeletal muscle tissue which are present in sensory nerve endings. Lips help retain food in the mouth as it is being chewed and play a role in phonation. The oral cavity contains the tongue and teeth ( see figure). Mammals can mechanically process a wide range of foods because their teeth are covered with enamel (the hardest material in the body) and because their jaws and teeth exert a strong force.


The oral cavity is consist of saliva, a watery fluid that secrete by least three pairs of salivary glands. Saliva help to moistens food, binds it with mucins (glycoproteins), and forms the ingested food into a moist mass called a bolus. Saliva also contains bicarbonate ions (HCO3), which buffer chemicals in the mouth, and thiocyanate ions (SCN) and the enzyme lysozyme, which kill microorganisms. It also contributes an enzyme (amylase) necessary for the initiation of carbohydrate digestion.


Saturday, 25 August 2018

Describes the process of digestion and absorbing in mammals?




Describes the process of digestion and absorbing in mammals?


The mammalian digestion and absorbing process consist of following tract;

1. Ingestion;      The process in which mammals  are eating.
2. Peristalsis;     The involuntary muscular contractions that move ingested nutrients towards the digestive tract.
3. Segmentation
;     In these process mixing the contents in the digestive tract.
4. Secretion
;       The release of hormones, enzymes, and specific ions and chemicals that take part in digestion.
5. Digestion
;        These part involve the conversion of large nutrient particles or
molecules into small particles or molecules.
6. Absorption
;       The passage of usable nutrient molecules from
the small intestine into the bloodstream and lymphatic system for the final passage to body cells.
7. Defecation
;       The elimination from the body of undigested
and unabsorbed material as waste.

Monday, 20 August 2018

What is respiratory pigment and give their types?



What is respiratory pigment and give their types?


Respiratory pigments are organic compounds that consist of metallic copper or iron that binds oxygen. These pigments may be in form of solution within the blood or body fluids, or they may be present in specific blood cells. These pigments respond to a high oxygen concentration by combining with oxygen and to low oxygen concentrations by releasing oxygen.
 The four most common respiratory pigments are hemoglobin, hemocyanin, hemerythrin, and chlorocruorin.

Hemoglobin
Hemoglobin is a reddish pigment that contains iron that bind to oxygen.
It is the most common respiratory pigment in animals and found in all vertebrates. Hemoglobin may be carried within red blood cells or simply dissolved in the blood or coelomic fluid.

Hemocyanin
Hemocyanin contains metallic copper and has a bluish color when oxygenated, and
always occurs dissolved in hemolymph. Hemocyanin is the most commonly occurring respiratory pigment in molluscs and certain crustaceans.  Hemocyanin  release oxygen easily and to provide a ready source of oxygen to the tissues as long as concentrations of oxygen in the environment are relatively high.

Hemerythrin
Hemerythrin contains iron and is pink when oxygenated. It is nucleated cells, rather than free in body fluids or hemolymph. Sipunculans, priapulids, a few brachiopods, and some polychaetes have hemerythrin.

Chlorocruorin
Chlorocruorin also contains iron but is green when associated with low oxygen concentrations and bright red when associated with high oxygen concentrations. Chlorocruorin occurs in several families of polychaete worms.

Friday, 17 August 2018

What is THE LYMPHATIC SYSTEM and give Their Function?




THE LYMPHATIC SYSTEM


The lymphatic system of vertebrate start with small vessels called lymphatic capillaries, which are in direct contact with the extracellular fluid surrounding tissues (see fig).


The system has four major functions:
(1) To collect and drain most of the fluid that drip from the bloodstream and accumulates in the extracellular fluid,
 (2)  Small amounts of proteins is return that have left the cells.
(3) To transport lipids that have been absorbed from the small intestine.
 (4) To transport foreign particles and cellular debris to disposal centers called lymph nodes.
 The small lymphatic capillaries merge to form larger lymphatic vessels called
lymphatics.
 Lymphatics are thin-walled vessels with valves that ensure the one-way flow of lymph. Lymph is the extracellular fluid that accumulates in the lymph vessels. These vessels pass through the lymph nodes on their way back to the heart. Lymph nodes concentrate in several areas of the body and play an important role in the body’s defense against disease.



What is Blood pressure? How to measure the blood pressure in human?




What is Blood pressure? How to measure the blood pressure in human?


Ventricular contraction generates the fluid pressure, called blood pressure, that forces blood through the pulmonary and systemic circuits. More specifically, blood pressure is the force the blood exerts against the inner walls of blood vessels.

Measurement


Before the measurement we known the types of blood pressure that are given below.

Systolic pressure

The maximum pressure achieved during ventricular contraction is called the systolic pressure.

Diastolic pressure

 When the ventricles relax the pressure of arterial decrease, and  remain pressure that exit in the arteries is called the diastolic pressure.
In humans, normal systolic pressure for a young adult is about 120 mm Hg, which is the amount of pressure required to make a column of mercury (Hg) in a sphygmomanometer rise 120 mm. Diastolic pressure is approximately 80 mm Hg. Conventionally, these readings are expressed as 120/80.

What is the HUMAN HEART and describe their Cardiac Cycle?




The HUMAN HEART and Their Cardiac Cycle


The human heart is a hard-working pump that moves blood through the body. It pumps its entire blood volume about 5 liters every minute; about 8,000 liters of blood move through 96,000 km of blood vessels daily. The heart of an average adult beats about 70 times per minute––more than 100,000 times per day.

Composition

The human heart is composed of cardiac muscle tissue that is called myocardium. The outer protective covering of the heart is composed of fibrous connective tissue called the epicardium. Connective tissue and endothelium form the inside of the heart, the endocardium.  

Part of Heart

The left and right halves of the heart are two separate pumps, each containing two chambers (See fig). In each half, blood first flows into a thin-walled atrium then into a thick-walled ventricle. Valves are between the upper (atria) and lower (ventricles) chambers. The tricuspid valve is presen b/w  right atrium and right ventricle, and the bicuspid valve is between the left atrium and left ventricle. Collectively, these are referred to as the AV valvesatrioventricular valves. The pulmonary semilunar valve is at the exit of the right ventricle, and the aortic semilunar valve is at the exit of the left ventricle.
All of these valves open and close when blood pressure changes when the heart contracts during each heartbeat. The function of valves in veins, heart valves keep blood moving in one direction, preventing backflow.



Cardiac Cycle

The heartbeat is a sequence of muscle contractions and relaxations called the cardiac cycle. A pacemaker a small mass of tissue called the sinoatrial node (SA node) at the entrance to the right atrium, initiates each heartbeat. Because the pacemaker is in the heart, nervous innervation is not necessary. The SA node initiates the cardiac cycle by producing an action potential that spreads along both atria, causing them to contract simultaneously. The action potential then passes to the atrioventricular node (AV node), near the interatrial septum.

From here, the action potential continues through the atrioventricular bundle), at the tip of the interventricular septum. The atrioventricular bundle divides into right and left branches, which are continuous with the Purkinje fibers in the ventricular walls. Stimulation of these fibers causes the ventricles to contract almost simultaneously and eject blood into the pulmonary and systemic circulations.

Process of cardiac cycle

During each Cardiac cycle, the atria and ventricles passes a phase of contraction called systole and a phase of relaxation called diastole. While the atria are relaxing and filling with blood, the ventricles are also relaxed.  Then more blood accumulates in the atria, blood pressure rises, and the atria contract, forcing the AV valves open and causing blood to rush into the ventricles. When the ventricles contract, the AV valves close, and the semilunar valves open, allowing blood to be pumped into the pulmonary arteries and aorta. After blood has been ejected from the ventricles, they relax and start the cycle a new.

What are Types of Circulatory Circuits?




Types of Circulatory Circuits


There are two types of circuits the pulmonary and systemic circuits.

Pulmonary circuit


Pulmonary circuit provides blood only to the lungs. It carries deoxygenated blood from the heart to the lungs, where carbon dioxide is removed, and oxygen is added. It then returns the oxygenated blood to the heart for distribution to the rest of the body.

Systemic circuit


The systemic circuit supplies all the cells, tissues, and organs of the body with oxygen-rich blood and returns oxygen-poor blood to the heart.



Thursday, 16 August 2018

TRANSPORT SYSTEMS of VERTEBRATES, CHARACTERISTICS OF VERTEBRATE, VERTEBRATE BLOOD VESSELS




TRANSPORT SYSTEMS of VERTEBRATES


All vertebrates have a closed circulatory system in which the walls of the heart and blood vessels are continuously contracted, and blood never leaves the blood vessels. Blood moves from the heart, through arteries, arterioles, capillaries, venules, veins, and back to the heart. Exchange between the blood and extracellular fluid only occurs at the capillary level.

CHARACTERISTICS OF VERTEBRATE

Vertebrate blood transports oxygen, carbon dioxide, and nutrients; defends against harmful microorganisms, cells, and viruses; prevents blood loss through coagulation (clotting); and helps regulate body temperature and pH. Because it is a liquid, vertebrate blood is classified as a specialized type of connective tissue. Like other connective tissues, blood contains a fluid matrix called plasma and cellular elements called formed elements.

Plasma


Plasma is the straw-colored, liquid part of blood. In mammals, plasma is about 90% water and provides the solvent for dissolving and transporting nutrients.
 A group of proteins (albumin, fibrinogen, and globulins) comprises another 7% of the plasma. The concentration of these plasma proteins influences the distribution of water between the blood and extracellular fluid.  Albumin about 60% of the total plasma proteins, it plays important roles to water movement. Fibrinogen is necessary for blood coagulation (clotting), and the globulins include the immunoglobulins and various metal-binding proteins.
Serum is plasma from which the proteins involved in blood clotting have been removed. The gamma globulin portion functions in the immune response because it consists mostly of antibodies. But 3% portion of plasma is consist of hormones, metabolic wastes, traces of many inorganic and organic molecules.
amino acids, glucose and other nutrients,  and various enzymes,

Formed Elements
The formed-element fraction (cellular component) of vertebrate blood consists of erythrocytes (red blood cells; RBCs), leukocytes (white blood cells; WBCs), and platelets (thrombocytes) (White blood cells are present in lower number than are red blood cells, generally being 1 to 2% of the blood by volume.

White blood cells are divided into agranulocytes (without granules in the cytoplasm) and granulocytes (have granules in the cytoplasm). The two types of agranulocytes are lymphocytes and monocytes. The three types of granulocytes are eosinophils, basophils, and neutrophils. Fragmented cells are called platelets
(thrombocytes). Each of these cell types is now discussed in more
detail.


Red Blood Cells

 Red blood cells vary dramatically in size, shape, and number in the different vertebrates. The RBCs of some vertebrates are nucleated, and mammalian RBCs are enucleated (without a nucleus). Some fishes and amphibians have enucleated RBCs. Some vertebrates such as the salamander has the largest RBC.
Avian RBCs are oval-shaped, nucleated, and larger than mammalian RBCs. Among birds, the ostrich has the largest RBC. Most mammalian RBCs are biconcave however, the camel and llama have elliptical RBCs. The shape of a biconcave disk provides a larger surface area for gas diffusion than a flat disk or sphere.  
Almost the entire mass of a RBC consists of hemoglobin, an iron-containing protein. The major function of an erythrocyte is to pick up oxygen from the environment, bind it to hemoglobin to form oxyhemoglobin, and transport it to body tissues. Blood rich in oxyhemoglobin is bright red.
 As oxygen diffuses into the tissues, blood becomes darker and appears blue when observed through the blood vessel walls. However, when this less oxygenated blood is exposed to oxygen, it instantaneously turns bright red. Hemoglobin also carries waste carbon  dioxide from the tissues to the lungs (or gills) for removal from the body.

White Blood Cells

 White blood cells are those blood cell that destroy microorganisms at infection sites, remove foreign chemicals, and remove debris that results from dead or injured cell.
Among the granulocytes, eosinophils are phagocytic, and ingest foreign proteins and immune complexes rather than bacteria. In mammals, eosinophils also release chemicals that counteract the effects of certain inflammatory chemicals released during allergic reactions. Basophils are the least numerous WBC. When they react with a foreign substance, their granules release histamine and heparin. Histamine causes blood vessels to dilate and leak fluid at a site of inflammation, and heparin prevents blood clotting. Neutrophils are the most numerous of the white blood cells.
They are chemically attracted to sites of inflammation and are active phagocytes. The two types of agranulocytes are the monocytes and lymphocytes.  
Two distinct types of lymphocytes are B cell and T cells, both of which are central to the immune response.
B cells originate in the bone marrow and colonize the lymphoid tissue, where they mature.
  T cells are associated with and influenced by the thymus gland before they colonize lymphoid tissue and play their role in the immune response. When B cells are activated, they divide and differentiate to produce plasma cells.


Platelets


Platelets or thrombocytes are disk-shaped cell fragments that initiate blood clotting. When a blood vessel is injured, platelets immediately move to the site and clump, attaching themselves to the damaged area, and thereby beginning the process of blood coagulation.

VERTEBRATE BLOOD VESSELS


Arteries are elastic blood vessels that carry blood away from the heart to the organs and tissues of the body. The central canal of an artery (and of all blood vessels) is a lumen. Surrounding the lumen of an artery is a thick wall composed of three layers, or tunicae.
Most veins are relatively inelastic, large vessels that carry blood from the body tissues to the heart. The wall of a vein contains the same three layers (tunicae) as arterial walls, but the middle layer is much thinner, and one or more valves are
present. The valves permit blood flow in only one direction, which is important in returning the blood to the heart.
Arteries lead to terminal
arterioles (those closest to a capillary). The arterioles branch to form capillaries (L. capillus, hair), which connect to venules and then to veins. Capillaries are generally composed of a single layer of endothelial cells and are the most numerous blood vessels in an animal’s body.
An abundance of capillaries makes an enormous surface area available for the exchange of gases, fluids, nutrients, and wastes between the blood and nearby cells.

What IS CHARACTERISTICS OF INVERTEBRATE?


CHARACTERISTICS OF INVERTEBRATE


 Some animals e.g., echinoderms, annelids, sipunculans use coelomic fluid as a supplementary or sole circulatory system. Coelomic fluid are identical to interstitial fluids or some time differ from this fluid, particularly with respect to specific proteins and cells. Coelomic fluids have the role to transports nutrients, and waste products and gases,. It have function in certain invertebrates (annelids) as a hydrostatic skeleton.

 Hemolymph is the circulating fluid of animals with an open circulatory system. Most arthropods, ascidians, and many molluscs have hemolymph.  These animals hve function to a heart pumps hemolymph at low pressures through vessels to tissue spaces and sinuses. Hemolymph  have high volume and the circulation slow. In the process of movement, essential gases, nutrients, and wastes are transported.

Many times, hemolymph has noncirculatory functions. For example, in insects, hemolymph pressure assists in molting of the old cuticle and in inflation of the wings. Some jumping spiders have hydrostatic pressure of the hemolymph that provides a hydraulic mechanism for limb extension.

The coelomic fluid, hemolymph, or blood of most animals contains circulating cells called blood cells or
hemocytes. Some cells contain a respiratory pigment, such as hemoglobin, and are called erythrocytes or red blood cells. These cells are usually present in high numbers to facilitate oxygen transport. Cells that do not contain respiratory pigments have other functions, such as blood clotting.

The number and types of blood cells vary dramatically in different invertebrates. For example, annelid blood contains hemocytes that are phagocytic. The coelomic fluid contains a variety of coelomocytes  such as amoebocytes, eleocytes, lampocytes, linocytes that have the role in phagocytosis, encapsulation, defense responses glycogen storage, , and excretion. Insect hemolymph contains large numbers of various hemocyte types that function in phagocytosis, encapsulation, and clotting.

What is Transport system in Invertebrates and give types of circulatory systems..?




Transport system in Invertebrates and types of circulatory systems


Transport system is the system in which different material, nutrients, and gases are transport from one part of the body to the other. Invertebrates transport system may be external and internal. We discussed following invertebrates transport system.

Protozoa

 Protozoa are small, with high surface-area-to-volume ratios all they need for gas, nutrient, and waste exchange is simple diffusion. In protozoa, the plasma membrane and cytoplasm are the connecting link through which materials diffuse to various parts of the organism, or between the organism and the environment.
Sponge
Some invertebrates have evolved specific transport systems. For example, sponges circulate water from the external environment through their bodies, instead of circulating an internal fluid.

Cnidarian

Cnidarians in which Hydra, have a fluid-filled internal gastrovascular cavity .This cavity provides nutrients for all body cells that lining the cavity, provides oxygen from the water in the cavity, and is a reservoir for carbon dioxide and other wastes. Simple body movement moves the fluid.
The gastrovascular cavity of flatworms, such as the planarian
Dugesia, is more complex than that of Hydra. In the planarian, branches penetrate to all parts of body.
Branched gastrovascular cavity runs close to all body cells, diffusion distances for nutrients, gases, and wastes are short. When body move than it distribute materials to several parts of the body.
Pseudocoelomate
Pseudocoelomate invertebrates, such as rotifers, gastrotrichs, and nematodes, use the coelomic fluid of their body cavity for transport. These animals are small, and body move against the coelomic fluids, which have direct link with the internal tissues and organs, produce adequate transport. A few other invertebrates e.g., ectoprocts, sipunculans, echinoderms also depend largely on the body cavity as a coelomic transport chamber.
Molluscs
Molluscs have transport functions that occur with a separate circulatory system. A circulatory or cardiovascular system is a specialized system in which a muscular, pumping heart moves the fluid medium called either hemolymph or blood in a specific direction determined by the presence of unidirectional blood vessels.
Types of circulatory system and their role in invertebrates
The animal kingdom has two basic types of circulatory systems: open and closed.

Open circulatory system,

 In an open circulatory system, the heart pumps hemolymph out into the body cavity or at least through parts of the cavity, where the hemolymph bathes the cells, tissues, and organs.

Closed circulatory system

 In a closed circulatory system, blood circulates in the confines of tubular vessels. The coelomic fluid of some invertebrates also has a circulatory role either in concert with, or instead of, the hemolymph or blood.
Role
The annelids, such as the earthworm, have a closed circulatory system in which blood travels through vessels delivering nutrients to cells and removing wastes.
Most molluscs and arthropods have open circulatory systems in which hemolymph directly bathes the cells and tissues rather than being carried only in vessels. For example, an insect’s heart pumps hemolymph through vessels that open into a body.

Tuesday, 7 August 2018

Endocrine System of Mammals and their Function---- Hormones?



Endocrine System of Mammals


Mammals have more complex endocrine system than other animals. Which consist of endocrine gland, organs, hormones and other target tissue.
A brief overview of mammalian endocrinology follows.

Pituitary Gland


The pituitary gland also called as the hypophysis which is directly present below the hypothalamus (see figure). The pituitary has two seperate lobes: the anterior lobe that is called adenohypophysis and the posterior lobe is called neurohypophysis.
 The two lobes differ in some ways:
(1) The adenohypophysis is larger than the neurohypophysis.
 (2)  Pituicytes is the secretery cells which are present in the adenohypophysis, but not present in the neurohypophysis.
(3) The neurohypophysis much more supply of nerve endings. Pituicytes also produce and secrete hormones from the adenohypophysis, whereas the neurohypophysis obtains their hormones from the neurosecretory cells that is present in the hypothalamus and storing and releasing them when they are needed. These hypothalamic nerve cells inter their axons to nerve cells and than blood vessels, into the pituitary gland, that directly linking the nervous and endocrine systems called the infundibulum.
The pituitary of many vertebrates instead of the humans, birds, and cetaceans also has a functional intermediate lobe (pars intermedia) that is mostly glandular tissue. It secrete hormone such as melanophore-stimulating hormone that have function to changes in the coloration of the body surface of many animals.

Hormones of the Neurohypophysis

The neurohypophysis obtain hormone from neurosecretory cells of the hypothalamus that synthesize and secrete two hormones, antidiuretic hormone and oxytocin. Where they are stored in the axon terminals until released.
Oxytocin have the function to mammalian reproduction by its effect on smooth muscle. It  also stimulates contraction of the uterus during pregnancy.

Hormones of the Adenohypophysis

The major endocrine portion of the pituitary is the adenohypophysis, which synthesizes six different hormones. All of these hormones are
polypeptides. The two hormones are nontropic which are growth hormone and prolactin.
Growth hormone (GH), or somatotropin (STH), does notinfluence a particular target tissue and affects all parts of the
body.
Prolactin (PRL) has the range of actions of the adenohypophyseal hormones. It plays an essential role in reproduction.
Thyrotropin, or thyroid-stimulating hormone (TSH), stimulates the thyroid gland’s synthesis and secretion of thyroxine, the main thyroid hormone.
Adrenocorticotropic hormone (ACTH) stimulates the adrenal gland to produce and secrete steroid hormones called glucocorticoids.

Thyroid Gland


The thyroid gland present in the neck, that is anterior to the trachea. These gland release thyroxine and triiodothyronine, both of which influence  growth, development, and metabolic rates. Thyroid gland also secerate, calcitonin hormone, that maintance levels of calcium ions (Ca2) by promoting the deposition of these ions into bone tissue when their concentrations rise. When calcium ions returns to its homeostatic concentration than thyroid cells decrease the secretion of calcitonin hormone.

Parathyroid Glands


The parathyroid glands are tiny, pea-sized glands that embedded in the thyroid lobes, each lobes have two glands. The parathyroids secrete parathormone (PTH), which regulates the concentrations of calcium (Ca2) and phosphate (HPO24) ions in the blood.
When the calcium concentration in the blood is low, PTH secretion increases and has the following effects: It stimulates bone cells to break down bone tissue and release calcium ions into the blood. It also enhances calcium absorption from the small intestine into the blood. Finally, PTH promotes calcium reabsorption by the kidney tubules to decrease the amount of calcium excreted in the urine.
Pancreas

The pancreas is an elongated, fleshy organ that is present posterior to the stomach. It functions both as an exocrine gland to secrete digestive enzymes and as an endocrine (ductless) gland.
 The endocrine portion of the pancreas contain about 1% of the gland. This endocrine portion synthesize, stores, and secretes hormones, in the form of cells cluster called pancreatic islets.
The pancreas contains 200,000 to 2,000,000
pancreatic islets. Each islet contains four special groups of cells, called alpha (), beta (), delta (), and F cells. The alpha cells produce the hormone glucagon, and beta cells produce insulin. The somatostatin hormone, hypothalamic growth secrete from the delta the hypothalamic growth-hormone inhibiting factor that also inhibits glucagon and insulin secretion. F cells release a pancreatic polypeptide that is released into the bloodstream when meal and inhibits somatostatin secretion, gallbladder contraction, and the secretion of pancreatic digestive enzymes.
When glucose concentrations in the blood is increase, such as after a meal, beta cells secrete insulin. Insulin increase the level of glucose into the body’s cells, including liver cells, where excess glucose can be converted to glycogen. Insulin and glucagon are crucial to the regulation blood glucose concentrations. When the blood glucose concentration is low, alpha cells secrete glucagon. Glucagon breakdown of glycogen into glucose units, which are than released into the bloodstream which raise the blood glucose concentration to the homeostatic level.


Gonads


The gonads contain ovaries and testes that secrete hormones that help regulate reproductive functions.  Male have the testes that secrete testosterone, which secrete luteinizing and follicle-stimulating hormones that produce by the adenohypophysis to stimulate spermatogenesis. Testosterone perform following function that growth and maintenance of the male sex organs, promotes the development and maintenance the level of sexual behavior, and in male, stimulates the growth of facial and pubic hair, and  enlargement of the larynx, which deepens the voice. The testes also produce inhibin, which inhibits the secretion of FSH.

Female produce thee following hormones that is necessary for female reproductive functions.
 Estrogens regulate the menstrual and estrus cycles and the development of the mammary glands and other female secondary sexual characteristics.
 The progestins also regulate the menstrual and estrus cycles, and the development of the mammary glands, that help in placenta formation during pregnancy.
 Relaxin, which is produced in small quantities, softens the opening of the uterus (cervix) at the time of delivery.
 The ovaries also produce inhibin, which inhibits the secretion of FSH.
Thymus
The thymus gland is present near the heart. It is large in young birds and mammals, but diminishes in size throughout adulthood.  Thymus glands produces peptide hormones, it contain thymopoietin (TP) and alpha1 and beta4 thymosin, that is essential for the normal development of the immune system.


Adrenal Glands
In mammals, two adrenal glands are present in the top of kidneys. Each gland contain two separate glandular tissues. The inner portion is the medulla, and the outer portion, that is surrounding the medulla, is the cortex.
Adrenal Cortex  
The adrenal cortex secretes three steroid hormones: glucocorticoids, mineralocorticoids (aldosterone), and sex hormones such as,androgens and estrogens. The glucocorticoids, such as cortisol, regulate metabolism
and the concentration of blood sugar.
 Aldosterone increase the rate of sodium reabsorption in the kidneys and, thus, water reabsorption, so, it plays a role to maintain the homeostasis of extracellular fluid.
 The sex hormones have a slight effect on male and female gonads. These sex hormones consist mainly of weak male hormones called androgens and lesser amounts of female hormones called estrogens.
Adrenal Medulla
 The adrenal medulla is under neural control. It contains neurosecretory cells that secrete  two hormone epinephrine and norepinephrine, which control heart rate and carbohydrate metabolism.
During times of excitement, emergency, or stress, the adrenal medulla contributes to the overall mobilization of the body through the sympathetic nervous system.

Saturday, 4 August 2018

What are the invertebrates hormones and their functions?




Invertebrates hormones


The survival of any group of animals depends on growth, maturation, and reproduction that consist of the most favorable seasons of the year so that climate and food supply are optimal. Thus, chemicals regulating growth, maturation, and reproduction probably were among the first hormones to appear during the course of animal evolution.
The first hormones were probably neurosecretions thus, the horomones that are present in invertebrate animals are neurosecretions called neuropseptides. In these invertebrates animal some more complex hormones are present. We are discusses following invertebrates hormones.

ANNELIDS

 Annelids contain the well developed nervous system, and circulatory system, and  also have a large coelom, their well-developed endocrine control of physiological functions is not surprising. Annelids Endocrine systems are perform following function with morphogenesis, development, growth, regeneration, and gonadal maturation. For example,
In leeches, a neuropeptide stimulates gamete development and triggers color changes. Osmoregulatory hormones have been reported in oligochaetes, and a hyperglycemic hormone that maintains a high concentration of blood glucose has been reported for the oligochaete, Lumbricus.
 Polychaetes, have juvenile hormone that inhibits the gonads and stimulates growth and regeneration. Another hormone, gonadotropin, stimulates the development of eggs.

PORIFERA
The porifera that also called sponges do not have special endocrine glands. So, sponges lack neurons, and do not have neurosecretory cells.

CNIDARIANS
The nerve cells of Hydra have a growth-promoting hormone that stimulates budding, regeneration, and growth. For example, when the hormone is present in the medium in which fragments of Hydra are incubated, “head” regeneration is accelerated. This so-called “head activator” also stimulates mitosis in Hydra.

MOLLUSCS
The ganglia have the ring that part the central nervous system of molluscs that secrete neurosecretory cells. This cells produce neuropeptides  that help to regulate heart rate, kidney
function,
and energy metabolism.
In some cephalopods, the optic gland in the eye stalk produces one or more hormones that increasse egg development, proliferation of spermatogonia, and also increase the development of secondary sexual characteristics.

Several gastropods, such as, land snail Helix, have the specific hormone stimulates spermatogenesis; one other hormone, termed egg-laying hormone, stimulates egg development; and hormones from the ovary and testis stimulate accessory sex organs. But In all snails, a growth hormone controls shell growth.

ECHINODERMS

 Echinoderms are deuterostomes, they are more closely related to the chordates and protostome invertebrates. But some endocrine systems of echinoderms provide produce hormone that are different from the chordate. However, that the radial nerves of sea stars consist of the a neuropeptide called gonad-stimulating substance. Neuropeptide hormone when inserted or injected into a adult sea star, it induces immediate shedding of the gametes, spawning behavior, and meiosis in the oocytes. The neuropeptide also release hormone  that is called maturation-inducing substance, which has various effects on the reproductive system.

NEMERTEANS
Nemerteans have a larger brain, that composed of a dorsal and ventral pair of ganglia connected by a nerve ring. The neuropeptide that these ganglia produce that control gonadal development and to regulate water balance.

NEMATODES
Nematodes do not have classical endocrine glands, they do have neurosecretory cells  that associated with the central nervous system. The neuropeptide that produces from this nervous tissue controls ecdysis of the old cuticle. But note this point neuropeptide are release only when a new cuticle is produced and stimulates the excretory gland to secrete an enzyme (leucine aminopeptidase) into the space between the old and new cuticle. The accumulation of fluid in this space causes the old cuticle to split and be shed.

PLATYHELMINTHS
Platyheminthes neurosecretory cells are identified in various flatworms over 30 years ago. Neurosecretory cells of this phylum are found in the cerebral major nerve cords and ganglion. The neuropeptides that the cells produce function in regeneration, asexual reproduction, and gonad maturation.
For example, neurosecretory cells  that are present in the scolex of some tapeworms control the shedding of the proglottids or the initiation of strobilization.

Endocrine systems of vertebrates and their hormones.




Endocrine systems of vertebrates


Endocrine system of vertebrates are more complex than invertebrates animals.
Following three aspects are known that are related of vertebrates animals
1.      Hormones (or neuropeptides) with the same function in different species may not be chemically identical.
2. Special hormones are species-specific according to their function that conversely in some hormones produced in one species may be completely functional in another species.
3. A hormone from one species may
responses a different functions in the same target cell or tissue of a different species.

Endocrine system in fishes

 The brain and spinal cord of fishes are produced more complex hormones, with other glands being rudimentary (see figure ).

 Three major regions in jawed fishes secrete neuropeptides. The two are present in the brain that are the
pineal gland of the epithalamus and the preoptic nuclei of the hypothalamus. The neuropeptides hormone  that produced by the pineal gland  influence the certain tissue pigment and inhibit reproductive development, both of which are stimulated by light.
Pineal glands also produces,the
melatonin hormone, has major effects on body metabolism perform activity patterns at the same time with light intensity and day length.
 The preoptic nuclei produce  different other type neuropeptides that control different functions in fishes for example, growth, sleep, locomotion. The third major region of fishes that has neuropeptide function is the urophysis.
The
urophysis is a distinct structure that are present in the tail of spinal cord. The urophysis produces  hormone neuropeptides that help blood pressure, control water, ion balance, , and smooth muscle contractions.
In many fishes, , hormones (e.g., melatonin) from the pineal gland control variations in skin color. When this hormone produced by one species is injected into another species, it can induce immediately color changes (see figure).
 Hormone prolactin that  also produced by the pituitary gland. Prolactin stimulates reproductive migrations in many animals (e.g., the movement of salamanders to water). Prolactin causes brooding behavior in some fishes. That control water and salt balances, and is essential for certain saltwater fishes to enter freshwater during spawning runs.
Some aquatic animals have several small ultimobranchial glands that form in ventral to the esophagus (see figure). These glands produce the hormone calcitonin that helps
controle the concentration of blood calcium.
Specialized endocrine cells (chromaffin tissue) or glands (adrenal glands)  that lie near the kidneys   and ready thesome vertebrates for stressful emergency situations. These tissues and glands produce two hormones epinephrine or adrenaline, and norepinephrine or noradrenaline that cause vasoconstriction increased blood pressure, changes in the heart rate, and increased blood glucose levels. These hormones are involved in the “fightor-flight” reactions.

Endocrine system in birds


In some birds such as pigeons and doves, the pituitary gland secretes the hormone prolactin. Prolactin stimulates the production of “pigeon’s milk” by sloughing off cells in the pigeon’s crop. Prolactin perform some function in birds such as they stimulates and regulates broodiness and certain other kinds of parental behavior, and along with estrogen, stimulates full development of the brood (incubation) patch (see figure)
. The brood patch helps keep the eggs at a temperature between 33 and 37° C.
The endocrine glands of birds contain the following part of hormone of the pituitary, thyroid, pancreas, parathyroids, pineal, hypothalamus, ovary, testes, adrenals,  thymus, ultimobranchial, and bursa of Fabricius.

The bird’s thyroid gland produces the hormone thyroxine. Thyroxine regulates  molt cycle, normal development of feathers and plays a role in the early stage of migratory behavior. In male birds, the testes produce the hormone testosterone. Testosterone controls the 2nd sexual characteristics of the male, such as, spurs, bright plumage color, comb
and —all of which strongly influence sexual behavior.
Dorsal of the cloaca have is a sac like structure of bursa of Fabricius that just lies it. . During the bird’s embryological development, it start to begins to shrink and than after hatching. Its tissues produce secretions that are responsible for the maturation of white blood cells (B lymphocytes), which play an important role in immunological reactions.
The ultimobranchial glands are small, paired structures in the neck just below the parathyroid glands. They secrete the hormone calcitonin, that perform the function to regulate blood calcium concentrations.