Zoology

1)Renin Angiotensinogen Aldosterone System : The functioning of the kidneys is efficiently monitored and regulated by hormonal feedback mechanisms involving the hypothalamus, JGA and to a certain extent, the heart.Osmoreceptors in the body are activated by changes in blood volume,body fluid volume and ionic concentration.An excessive loss of fluid from the body can activate these receptors which stimulate the hypothalamus release antidiuretic hormone (ADH) or vasopressin from the neurohypophysis. ADH facilitates water reabsorption from latter parts of the tubule, thereby preventing diuresis. An increase in body fluid volume can switch off the osmoreceptors and suppress the ADH release to complete the feedback. ADH can also affect the kidney function by its constrictory effects on blood vessels. This causes an increase in blood pressure. An increase in blood pressure can increase the glomerular blood flow and thereby the GFR.The JGA plays a complex regulatory role. A fall in glomerular...

Urine formation involves three main processes namely, glomerular filtration, reabsorption and secretion, that takes place in different parts of the nephron. The first step in urine formation is the filtration of blood, which is carried out by the glomerulus and is called glomerular filtration. On an average, 1100-1200 ml of blood is filtered by the kidneys per minute which constitute roughly 1/5th of the blood pumped out by each ventricle of the heart in a minute. The glomerular capillary blood pressure causes filtration of blood through 3 layers, i.e., the endothelium of glomerular blood vessels, the epithelium of Bowman’s capsule and a basement membrane between these two layers. The epithelial cells of Bowman’s capsule called podocytes are arranged in an intricate manner so as to leave some minute spaces called filtration slits or slit pores. Blood is filtered so finely through these membranes, that almost all the constituents of the plasma except the proteins pass onto...

Structure of nephron Each kidney has nearly one million complex tubular structures called nephrons (Figure), which are the functionalunits. Each nephron has two parts – the glomerulus and the renal tubule. Glomerulus is a tuft of capillariesformed by the afferent arteriole – a fine branch of renal artery. Blood from the glomerulus is carried away by an efferent arteriole.The renal tubule begins with a double walled cup-like structure called Bowman’s capsule, whichencloses the glomerulus. Glomerulus alongwith Bowman’s capsule, is called the malpighian body or renal corpuscle (Figure). The tubule continues further to form a highly coiled network – proximal convoluted tubule (PCT). A hairpin shaped Henle’s loop is the next part of the tubule which has a descending and an ascending limb. The ascending limb continues as another highly coiled tubular region called distal convoluted tubule (DCT). The DCTs of many nephrons open into a straight tube called collecting duct, many of w...

Cerebrum is the most developed and 2/3 part of the total brain 1.Cerebrum consist of two cerebral hemispheres. On the dorsal surface, a longitudinal groove deep clefti present between two cerebral hemispheres called as median fissure. Both the cerebral hemispheres are partially connected with each other by a curved thick band (tract) of nerve fibres called corpus callosum Largest commisure and specific character of mammalian brain)  2.Each cerebral hemisphere is divided into 4 lobes-Anterior, middle, posterior and lateral. Anterior lobe is also called frontal lobe largest lobe. Middle lobe is also called parietal lobe 3. Central sulcus separates frontal lobe from parietal lobe. Lateral lobe or temporal lobe is separated from frontal lobe and parietal lobe by incomplete sulcus called lateral sulcus Posterior lobe is abo called occipital lobe. It is separated from parietal lobe by a sulcus called parieto occipital sulcus 4. Many ridges and grooves are found on dorsal surf...

Different stage of nerve conduction (1) Polarisation (Resting stage) (2) Depolarisation (Excited stage) (3) Repolarisation (again resting stage) 1) POLARISATION Neurons are excitable cells because their membranes are in a polarised state. Do you know why the membrane of a neuron is polarised? Different types of ion channels are present on the neural membrane. These ion channels are selectively permeable to different ions. When a neuron is not conducting any impulse, i.e.. resting, the axonal membrane is comparatively more permeable to potassium ions (K*) and nearly impermeable to sodium ions (Na+). Similarly, the membrane is impermeable to negatively charged proteins present in the axoplasm. Consequently, the axoplasm inside the axon contains high concentration of K* and negatively charged proteins and low concentration of Nat. In constrast, the fluid outside the axon contains a low concenration of K a high concentration of Na* and thus from a concentration gradient. These ...