Kidney is divided into
outer cortex and inner medullary region.
The cortical portion that projects between the
medullary pyramids are known as columns of Bertini.
Nephrons are basic functional units of kidney.
Malpighian body or renal
corpuscle comprises
of Bowman’s capsule and glomerulus.
Malpighian body, Proximal
Convoluted Tubule (PCT), and Distal Convoluted Tubule (DCT) are located in
the cortical region of kidney.
Loop of Henle’s is found in the
medullary region of kidney.
Vasa recta – It is a loop of
capillaries that runs parallel to Henle’s loop.
Afferent arteriole: The
arterioles that breaks into numerous capillaries to form glomerulus present
inside the Bowman's capsule.
Efferent arteriole: Emerging from
the Bowman's capsule these capillaries combines together and travels a short
distance and break up into the secondary capillary network.
Excretory organ in various animals
·
Protonephridia (flame cells): Examples, platyhelminthes, rotifers and some annelids
·
Amphioxus
is a chordate that has flame cells.
·
Nephridia: Example,
earthworm
·
Malpighian tubules: Examples, insects such as cockroach
·
Antennal glands (green gland): Examples, crustacean such as prawns
·
Urine formation
It involves three process:
1.
Glomerular filtration - Filtration of water and dissolved substances out of the
blood in the glomeruli and into Bowman's capsule
2.
Reabsorption - Reabsorption of water and dissolved substances out of
the kidney tubules back into the blood. This process prevents substances
required by the body from being lost in the urine.
3.
Secretion - Secretion of hydrogen ions (H+), potassium ions (K+),
ammonia (NH3), and certain drugs out of the blood and into the kidney tubules,
where they are eventually eliminated in the urine
·
Glomerular filtration rate: It is the amount of glomerular filtrate formed in all
nephrons of both kidneys per minute.
It is about 125 mL/ minute in a healthy individual.
Regulation of glomerular filtration rate is auto
regulative. It is carried out by juxtaglomerular apparatus.
About 99% of filtrate is reabsorbed by renal tubule.
Glucose, amino acids, and sodium are actively absorbed.
Nitrogenous wastes and water are reabsorbed passively
from filtrate.
·
Descending limb of Henle’s loop is permeable to water and impermeable to electrolytes.
·
Ascending limb of Henle’s loop is impermeable to water.
·
Distal convoluted tubule involves reabsorption of sodium ions.
·
Counter current mechanism
-
It is an
adaptation for conservation of water.
-
Two
current mechanisms operating in kidney are – Henle’s loop and vasa rectae. They
both help in maintaining a concentration gradient in the medullary
interstitium.
Regulation of Kidney
·
Juxtaglomerular
apparatus contains juxtaglomerular cells that release renin.
· Renin – Angiotensin mechanism
·
Anti-diuretic hormone (Vasopressin) secreted by
neurohypophysis facilitates water reabsorption from distal convoluted tubule
and collecting duct. Hence, it is quite important for the process of
osmoregulation.
·
Atrial natriuretic factor (ANF) keeps a check on renin-angiotensin mechanism.
-
Uremia – Accumulation
of urea in blood. It can be cured by performing haemodialysis.
·
Renal failure – It is the condition when the kidney loses the ability
to form urine and concentrate it. It can be corrected by kidney transplantation
method.
·
Renal calculi –Accumulation of insoluble crystallised salts within the
kidney
·
Glomerulonephritis – Inflammation of glomeruli
·
Glycosuria – Presence of glucose in urine
·
Ketonuria – Presence
of ketone bodies in urine
