BSN PHYSIOLOGY: RENAL SYSTEM

 Substantial topics :  

• Functions of kidney? jaypee pg#325
• Juxtaglomerular apparatus & its functions?
• Autoregulation 
• Glomerular filtration rate (GFR)
• Explain how body water and electrolyte balance is maintained?
• Functions of ureters,urethra
• Spinobulbospinal reflex?
• Effects of aging on the urinary system?
• Summary of urine formation?
• Voluntary control of micturition? Pg#342 
• Pathophysiology:
• Diseases of the kidney;
• Outline the principal effects of glomerulunephritis?
• Stages of development of nephrotic syndrome?
• Effects of diabetes mellitus and hypertension on kidney function?
• Discuss the sources and cosequences of kidney functions?
• Pathogenesis of kidney stones? 
• Development and spread of common kidney tumors? 
• IMPORTANT FIGURES:

Fig#13.1+Fig#13.2,Fig#13.3,Fig#13.4+Fig#13.7,Fig#13.9,Fig#13.10,Fig#13.11,Fig#13.12,Fig#13.13,Fig#13.14,Fig#13.15,Fig#13.16,Fig#13.17+13.19+13.20+13.21+13.22+13.23

Table # 13.1+13.2+13.3.                        BOX# 13.1+13.2.                                         An overview of renal physiology:   Renal system includes:                              1. A pair of kidneys .                                  2. Ureters                                                       3. Urinary bladder.                                     4. Urethra. 

Both the kidneys receive about 1,300 mL of blood per minute, i.e. about 26% of cardiac output. Kidneys are the second organs to receive maximum blood flow, the first organ being the liver, which receives 1,500 ml per minute, i.e. about 30% of cardiac Output

Functions of kidney:

1. ROLE IN HOMEOSTASIS:                     a) Excretion of Waste Products(urea,uric acid,creatinine,bilirubin)                          b) Maintainance of water balance.          c) Maintenance of Electrolyte Balance      d) Maintenance of Acid–Base Balance

2-HEMOPOIETIC Function                      3. ENDOCRINE FUNCTION(Hormones secreted by kidneys                                      i. Erythropoietin                                         ii. Thrombopoietin                                     iii. Renin                                                       iv. 1,25-dihydroxycholecalciferol (calcitriol)                                                       v. Prostaglandins

4.REGULATION OF BLOOD PRESSURE(through renin angiotensin mechanism)

 5. REGULATION OF BLOOD CALCIUM LEVEL

Functional unit of kidney (Nephron) 

Role of nephron:                                       A. Glomerular filtration                           B. Tubular reabsorption.                          C. Tubular secretion

Filteration:

Glomerular filtration is the process by which the blood is filtered while passing through the glomerular capillaries by filtration membrane Occurs by fenestrations.Only small particles and proteins can pass through it. (4nm-8nm in size) .Mesangial cells in the filteration membrane contract to regulate the rate of filteration.

JUXTAGLOMERULAR APPARATUS:

At the juncture where the afferent and efferent arterioles enter and leave Bowman’s capsule, the initial part of the distal convoluted tubule (DCT) comes into direct contact with the arterioles(JGA).

MACCULA DENSA:                                  The wall of the DCT at that point forms a part of the JGA known as the macula densa. A second function of the macula densa cells is to regulate renin release from the juxtaglomerular cells of the afferent arteriole.                Functions:This cluster of cuboidal epithelial cells also monitors the fluid composition of fluid flowing through the DCT.A second cell type in the lining of afferent artriole is the juxtaglomerular cell that can contract or relax in response to ATP or adenosine released by the macula densa. Such contraction and relaxation regulate blood flow to the glomerulus and filteration occurs.

‘Glomerular filtration rate (GFR):

GFR is defined as the total quantity of filtrate formed in all the nephrons of both the kidneys in the given unit of time.                                                       Normal GFR is 125 mL/minute or about 180 L/day”.                                              How GFR is regulated?                              If the osmolarity of the filtrate is too high (hyperosmotic), the juxtaglomerular cells will contract, decreasing the glomerular filtration rate (GFR) so less plasma is filtered, leading to less urine formation and greater retention of fluid. This will ultimately decrease blood osmolarity toward the physiologic norm. 

 The net result of these opposing actions is to keep the rate of filtration relatively constant.                                              Function of JGA:                                          1. Renin.                                                         2. Prostaglandin                          mesangial cells of juxtaglomerular apparatus secrete cytokines like interleukin-2 and tumor necrosis factor Macula densa of juxtaglomerular apparatus plays an important role in the feedback mechanism which regulates the renal blood flow and glomerular filtration rate 

SELECTIVE REABSORPTION:

 Tubular reabsorption is the process by which water and other substances are transported from renal tubules back to the blood.                                                Large quantity of water (more than 99%), electrolytes and other substances are reabsorbed by the tubular epithelial cells.The substances that are reabsorbed, move into the interstitial fluid of renal medulla.And, from here, the substances move into the blood in peritubular capillaries.

Tubular reabsorption is known as selective reabsorption because the tubular cells reabsorb only the substances necessary for the body.such as glucose, amino acids and vitamins are completely reabsorbed from renal tubule.

Secretion:

Whereas the unwanted substances like metabolic waste products are not reabsorbed and excreted through urine. Collecting ducts merge as they descend deeper in the medulla to form about 30 terminal ducts, which empty at a papilla. They are lined with simple squamous epithelium with receptors for ADH. When stimulated by ADH, these cells will insert aquaporin channel proteins into their membranes, which as their name suggests, allow water to pass from the duct lumen through the cells and into the interstitial spaces to be recovered by the vasa recta.

This process allows for the recovery of large amounts of water from the filtrate back into the blood. 

In the absence of ADH:                        these channels are not inserted, resulting in the excretion of water in the form of dilute urine. 

NERVE SUPPLY TO URINARY BLADDER AND SPHINCTERS :

Urinary bladder and the internal sphincter are supplied by sympathetic and parasympathetic divisions of autonomic nervous system where as, the external sphincter is supplied by the somatic nerve fiber. 

1-SYMPATHETIC NERVE SUPPLY:

Preganglionic fibers of sympathetic nerve arise from first two lumbar segments (L1 and L2) of spinal cord. 

After leaving spinal cord, the fibers pass through lateral sympathetic chain without any synapse in the sympathetic ganglia and finally terminate in hypogastric ganglion.

 The postganglionic fibers arising from this ganglion form the hypogastric nerve, which supplies the detrusor muscle and internal sphincter. 

Function of Sympathetic Nerve 

The stimulation of sympathetic (hypogastric) nerve causes relaxation of detrusor muscle and constriction of the internal sphincter. It results in filling of urinary bladder and so, the sympathetic nerve is called nerve of filling. 

2- PARASYMPATHETIC NERVE SUPPLY 

Preganglionic fibers of parasympathetic nerve form the pelvic nerve or nervus erigens. Pelvic nerve fibers arise from second, third and fourth sacral segments (S1, S2 and S3) of spinal cord. These fibers run through hypogastric ganglion and synapse with postganglionic neurons situated in close relation to urinary bladder and internal sphincter. 

Function of Parasympathetic Nerve:

Stimulation of parasympathetic (pelvic) nerve causes contraction of detrusor muscle and relaxation of the internal sphincter leading to emptying of urinary bladder. So, parasympathetic nerve is called the nerve of emptying or nerve of micturition.                                      Pelvic nerve has also the sensory fibers, which carry impulses from stretch receptors present on the wall of the urinary bladder and urethra to the central nervous system. 

3-SOMATIC NERVE Supply:           External sphincter is innervated by the somatic nerve called pudendal nerve. It arises from second, third and fourth sacral segments of the spinal cord. 

--->Diseases of the kidneys(pg#350-357).

So these are fundamental stuff you need to know about it.