Kidney & Micturition Reflex Dr. Wasif Haq

Daily Water Intake & Loss Total water intake= 2300 ml/day (2100 ml from diet & 200 ml metabolic byproduct) Daily loss=2300 ml/day (Insensible loss 700 ml,, Sweat=100 ml, Feces=100ml, Urine=1400 ml)

Anatomy of Kidney Retroperiotoneal organ. Each kidney has indentation on medial aspect called “Hilum” ; renal artery & vein, nerves, lymphatics & ureter pass. Upon bisection: 1. Outer cortex 2. Inner Medulla. Cortical nephron: Lying close to cortex, short Loop of Henle. Juxta-medullary nephron: At border of cortex & medulla with tubular system penetrating deep in inner medulla, have long Loop of Henle and additional capillaries called “Vasa recta”. Help in formation of concentrated urine.

Medulla (divide in cone shaped masses called) Renal Pyramids (which terminate in) Papilla (that project into) Renal Pelvis Upper border of Pelvis (divide in open pouches called) Major Calices (Extend downward & divide into) Minor Calices ( Collect urine from Papilla)

Calices, Pelvis & Ureter push Urine to bladder.

Segments of Nephron Nephron Glomerulus (Ball of capillaries, fluid filtration occurs) Tubules (Filtered fluid converted to urine) Filtration Pathway: Glomerulus (Enclosed in Bowman’s capsule) Bowman’s capsule Proximal tubule Loop of Henle (a)Ascending limb(b)Descending limb. Thick ascending limb Distal tubule Connecting tubule Cortical collecting tubule Cortical collecting duct Medullary collecting duct Papilla Pelvis

Renal Blood & Nerve Supply 22% of cardiac output. 1100ml/min. Right and left renal artery from Abdominal Aorta. Renal artery Interlobar artery Arcurate arteries Interlobular arteries Afferent arterioles Glomerulus Efferent arterioles Peritubular capillaries Interlobular vein Arcurate vein Interlobar vein Renal vein Nerve supply: Sympathetic supply. Sensory input T level of spinal cord.

Functions of Kidney 1. Excretion of metabolites (Urea, Uric acid, Bilirubin & Creatinine) 2. Water & Electrolyte balance (Intake must match the output; adjustments for H 2 0, Na +, Cl -, Ca ++, H +, K + etc 3. Arterial pressure regulation 4. Acid base balance (Excretion of acids produced during protein metabolism) 5. Erythrocyte production 6. Active form of Vitamin D (1,25-dihydroxyvitamin D 3 ) 7. Gluconeogenesis in periods of starvation.

Micturition Reflex & Abnormalities

Micturition & Urinary Bladder “Emptying of urinary bladder when it is filled”. An autonomic spinal cord reflex with control by cerebral cortex. Urinary bladder : a. Body (urine collection), b. Neck (connects to Urethra). Detrusor: Smooth muscle of bladder, contraction causes emptying. Fusion with similar muscle fibers. Two sphincters: a. Internal (in bladder neck), b. External (behind posterior urethra).

Innervations Pelvic nerve through Sacral plexus (S2-3) having sensory & motor fibers. Sensory: Degree of stretch in bladder wall & initiate micturation reflex. Motor: Parasympathetic fibers innervating Detrusor. Pudendal nerve: External bladder sphincter. Sympathetic innervations by Hypogastric nerve controls the blood vessels, pain & fullness sensation conveyed.

Micturition Reflex Self regenerative reflex & fatigable. Stretch of sensory receptors in bladder wall convey afferent impulses to Sacral segment of Spinal Cord by Pelvic nerve, Parasympathetic fibers bring efferent impulses. If bladder partially filled; Detrusor relaxes after some micturation contractions. Strong micturation reflex causes reflex inhibition of constriction on External bladder sphincter through Pudenal nerve.

Control By Higher Center Strong facilitative & inhibitory center in brain stem (pons) Mostly inhibitory center in cortex, can become excitatory. Urination only when constriction of External sphincter inhibited. Contraction of abdominal muscles pushes urine towards urethra and bladder stretching their walls.

Abnormalities If sensory fibers from bladder to spinal cord damaged: Bladder control lost, bladder fills to capacity & overflows leaking urine. Weak bladder muscles cause incomplete emptying of bladder called Overflow incontinence. Spinal cord injury above Sacral segment leaving Sacral segment intact: Automatic bladder. Involuntary urination. Partial damage to spinal cord & brainstem: Uninhibited neurogenic bladder. Inhibitory signals lost. Frequent involuntary urination even by small volume of urine.