Function and structure of the kidneys Flashcards
What are the functions of the kidneys? Name 5
- Regulating water concentration, inorganic ion composition, acid-base balance and the fluid volume of internal environment.
- Excrete metabolic waste products into the urine. Ensures that waste products which are toxic do not accumulate in the body.
- Urinary excretion of foreign chemicals such as: drugs, pesticides, and food additives and their metabolites.
- Gluconeogenesis - during prolonged fasting, the kidneys synthesize glucose from amino acids and other precursors and release it into the blood.
- Act as endocrine glands - releasing at least 2 hormones, EPO and 1, 25 - dihydroxyvitamin D. They also secrete an enzyme, renin that is important in the control of BP and sodium balance.
Look at the structure of the kidneys
The kidney is divided into an outer renal cortex and the inner renal medulla.
The outer portion, cortex, contains all the renal corpuscles. The loops of Henle extend from the cortex for varying distances down into the medulla.
The medullary collecting ducts pass through medulla on their way to the renal pelvis.
Look at the structure of a nephron
Each nephron contains of
(1) An initial filtering component called the renal corpuscle
(2) A tubule that extends from the renal corpuscle
What are the 2 types of nephrons?
(1) Juxtamedullary nephrons - around 15%. Nephrons where the renal corpuscle lies in the part of the cortex closest to the cortical-medullary junction. The Loop of Henle of these nephrons plunge deep into the medulla
(2) Cortical nephrons - the majority of nephrons are cortical. Meaning the renal corpuscle is located in the outer cortex and their Loop of Henle’s do not plunge deep into the medulla.
Look at the structure of the Renal Corpuscle
The renal corpuscle includes:
(1) Bowman’s Capsule, afferent and efferent arterioles
(2) glomerulus/glomerular capillaries.
What type of filtrate does the renal corpuscle form? What happens as it passes through the tubules?
It forms a filtrate from blood that is free of cells, large polypeptides and proteins. This filtrate leaves the renal corpuscle and enters the tubule.
As it passes through the tubules, substances are added to or removed from it. Ultimately, the fluid remaining at the end of each nephron combines in the collecting ducts and exits the kidneys as urine.
What type of blood enters the renal corpuscle and what type leaves?
Unfiltered blood enters the Renal corpuscle via the afferent arterioles. As blood flows through the glomerulus/glomerular capillaries, about 20% of the plasma filters into the Bowman’s Capsule. The remaining blood then leaves the glomerulus by the efferent arteriole.
What are the 3 layers which separate the blood in the glomerulus from the blood in Bowman’s Capsule?
(1) Single-celled capillary endothelium
(2) A non-cellular proteinaceous layer of the basement membrane
(3) Single-celled epithelial lining of bowman’s capsule - Podocytes.
Fluid filters across the endothelial cells, then through the basement membrane, and finally between the foot processes of the podocytes.
Name the different tubules in the nephron
Proximal convoluted tubule
Loop of Henle - descending and ascending limb
Distal convuluted tubule
Collecting ducts
What are peritubular capillaries and what do they do?
All along the tubules, they are surrounded by peritubular capillaries.
They allow rebasoprtion and secretion between the inner lumen of the nephron and capillaries. The capillaries then re-join to form the veins by which blood leaves the kidneys.
What is the juxtaglomerular apparatus?
As the ascending limb of Henle passes between the afferent and efferent arterioles of its nephron, there is a patch of cells in the wall of the ascending limb as it becomes the distal tubule called macula densa cells. There are juxtaglomerular cells in the wall of hte afferent arteriole.
The combination of macula densa and juxtaglomerular cells is known as the juxtaglomerular apparatus.
