1. Irfan Idris Physiology Department, Medical Faculty, UNHAS
Physiology of kidney
Irfan Idris
Physiology Department, Medical Faculty, UNHAS

2. Objectives With the end of this session you are be able to :
have knowledge of physiologic anatomy of the kidneys
understand how kidney creates urine
understand filtration & tubular transport process
have knowledge about role of tubuloglomerular feedback

3. Physiologic anatomy of the kidneys

5. Blood Supply Interlobular vein Interlobular artery Renal pelvis
Renal artery
Renal vein
Ureter
Cortex
Medulla
Arcuate vein
Arcuate artery

6. Renal artery  interlobar artery  arcuate artery  interlobular artery  afferent arteriole  glomerulus  efferent arteriole  peritubular artery  vasa recta  vv. peritubular  arcuate vein  interlobar vein  renal vein

9. NEPHRON
Nephron is a functional unit of kidney. Each kidney consists of about one million nephrons. The tubule is made up of a number of sections, the proximal tubule, the medullary loop (loop of Henle), and the distal tubule which finally empties into the collecting duct.

11. URINE FORMATION

13. Filtration and tubular transport
Filtration : a fluid that resembles plasma is filtered through the glomerular capillaries into the renal tubules
Molecules with a radius of r <1.8 nm (molecular mass < Da) freely pass through the filter,
While those with a radius of r > 4.4nm (molecular mass >80 000DA, e.g., globulins) normally cannot pass through.
Only a portion of molecules where 1.8 nm < r < 4.4nm applies are able to pass through the filter.
Negatively charged particles (e.g., albumin: r = 3.4 nm) are less permeable than neutral substances of equal radius because negative charges on the wall of the glomerular filter repel the ions.

14. The GFR in an average-sized normal man is approximately 125 mL/min
GFR = Kf x (pG – pB – G + B)

20. Transport of Substances Through the Cell Membrane

21. Transport of Substances Through the Cell Membrane
Active Transport
Passive Transport

22. Active transport Primary active transport Secondary active transport
Ion Pump
Secondary active transport
Co transport
Counter transport

24. Passive Transport
Simple diffusion
Facilitated diffusion

25. SGLT-2
SGLT-1

26. PepT2
PepT1/2

31. Role of Tubuloglomerular Feedback
The tubuloglomerular feedback (1) an afferent arteriolar feedback mechanism and (2) an efferent arteriolar feedback mechanism  arrangements of the juxtaglomerular complex
The juxtaglomerular complex consists of macula densa cells in the initial portion of the distal tubule and juxtaglomerular cells in the walls of the afferent and efferent arterioles.

36. Acid base
The lungs and kidneys work together to produce a normal extracellular fluid and arterial pH of
The kidney excretes fixed acid and performs three functions to achieve this 1)Tubular secretion of acid 2) Glomerular filtration of buffers which combine with H+ 3) Ammonia is produced enzymatically from glutamine and other amino acids, and is secreted in the tubules

39. Excretion of waste products
Filtration occurs as blood flows through the glomerulus. Some substances not required by the body, and some foreign materials (e.g. drugs) may not be cleared by filtration through the glomerulus. Such substances are cleared by secretion into the tubule and excreted from the body in the urine

40. Hormones and the Kidney
Renin (see above) increases the production of angiotensin II which is released when there is a fall in intravascular volume e.g. haemorrhage and dehydration.
Aldosterone promotes sodium ion and water reabsorption in the distal tubule and collecting duct where Na+ is exchanged for potassium (K+) and hydrogen ions by a specific cellular pump.

41. Atrial Natruretic Peptide(ANP) is released when atrial pressure is increased e.g. in heart failure or fluid overload. It promotes loss of sodium and chloride ions and water chiefly by increasing GFR.
Antidiuretic Hormone (ADH) increases the water permeability of the distal tubule and collecting duct, thus increasing the concentration of urine.

42. The hormones interact when blood loss or dehydration occurs to maintain intravascular volume. The flow diagram (left) illustrates this

43. Other Substances Produced by the kidney
1,25 dihydroxy vitamin D (the most active form vitamin D) which promotes calcium absorption from the gut.
Erythropoietin which stimulates red cell production

44. Micturition
Process by which the urinary bladder empties when it becomes filled
First, the bladder fills progressively until the tension in its walls rises above a threshold level
this elicits the second step, which is a nervous reflex called the micturition reflex that empties the bladder or, if this fails, at least causes a conscious desire to urinate.
Although the micturition reflex is an autonomic spinal cord reflex, it can also be inhibited or facilitated by centers in the cerebral cortex or brain stem

45. Blood vessels and have little to do with bladder contraction.
Some sensory nerve fibers also pass by way of
the sympathetic nerves and may be important in the
sensation of fullness and, in some instances, pain.
The sensory fibers : degree of stretch in the bladder wall, reflexes that cause bladder emptying.
The motoric fibers : innervate wall of the ballder and the detrusor muscle. Also Most important are the skeletal motor fibers transmitted through the pudendal nerve to the external bladder sphincter. These are somatic nerve fibers that innervate
and control the voluntary skeletal muscle of the sphincter

46. As a summary  Functions of the Kidney
Regulation of the water and electrolyte content of the body.
Retention of substances vital to the body such as protein and glucose
Maintenance of acid/base balance.
Excretion of waste products, water soluble toxic substances and drugs.
Endocrine functions. 

47. Recommended references
Textbook of Medical Physiology, 11th edition, Guyton & Hall, Elsevier Saunders, 2006
Review of Medical Physiology,, 21th edition, WF. Ganong, McGraw-Hill Company, 2003

48. Thank you