L2 - Urinary production and Micturition

What are functions of Kidney?

Regulate fluid + electrolyte levels, osmolarity, pH

Regulate blood pressure

Produce vitamin D

Waste excretion

How much cardiac output does kidney receive?

25% by renal arteries

What are the branches of the renal artery?

Segmental arteries → Lobar arteries → Interlobar arteries → Arcuate arteries → Interlobular arteries

What species have unilobular kidneys?

Cats and dogs

Where do the lobar arteries go?

Into different kidney lobes

Which arteries branch between medulla and cortex?

Arcuate arteries

Which arteries connect to afferent arterioles?

Interlobular arteries

What does a dog kidney look like?

Bean, unilobular shaped (cortex and medulla fused) with smooth exterior

Where are kidneys located?

Right = L1-3

Left = L2-4

How much of glomerular filtrate is reabsorbed at PCT?

70%

(some water and electrolytes, all glucose)

What makes up the renal corpuscle?

Bowman’s capsule and glomerulus

What layers does filtrate cross to leave blood?

Endothelium (by pores)

Podocytes (by filtration slits)

What are Pedicels?

Podocyte processes that wrap around capillaries forming filtration slits

How is blood filtered?

Based on size and charge of molecule

What is colloid osmotic pressure?

Proteins retained in blood form gradient to reabsorb water

What is Net Filtration Pressure (NFP)?

Forces water and solutes through filter at Bowman’s capsule

What is hydrostatic pressure?

Pressure exerted by fluid in confine space

Why must the Glomerular filtrate rate (GFR) be regulated and how?

Maintain homeostasis and blood pressure

Intrinsic and extrinsic regulation

What are the 2 instrinsic autoregulation mechanisms?

Myogenic mechanism and Tubuloglomerular feedback

What is Myogenic mechanism?

Afferent arteriole stretch and contracts causing vasoconstriction, decreasing glomerulus blood flow to maintain GFR + NFP

What is Tubuloglomerular feedback?

Macula densa (MD) cells in DCT sense flow rate and Na+ concentration.

MD cells release ATP + adenosine to signal juxtaglomerular cells in afferent arteriole to vasoconstrict

What are Extrinsic regulations?

SNS cause vasoconstriction + decrease GFR

Adrenal gland Epinephrine cause vasocontriction (fight or flight)

Renin Angiotensin Aldosterone System (RAAS)

What is PCT function?

Glucose, peptide, amino acid selective reabsorption

Homeostasis

How is PCT surface area increase?

Villi and microvilli

What is polyuria?

Frequently urinating

What are aquaporins and function?

Water channels/pores in membrane

Differ between different parts of nephron

How does water diffuse out descending limb of loop of Henle?

Electrolytes surrounding draw water out down osmotic gradient

What happens at ascending limb of loop of Henle?

Na+, Cl-, K+ actively pumped out by cotransporter

Wall impermeable to water

What is DCT function?

Selective reabsorption of filtrate

Acid-base balance

Homeostasis

What is collecting duct functions?

Drain filtrate DCT to renal pelvis

Reabsorb salt + water mediated ADH

Acid-base balance

Define Micturiton

Bladder distend lead to coordinated expulsion of contents

Modified by conscious control

What is the Urethralis muscle?

Skeletal muscle surround urethra pelvic part

Act as external urethral sphincter

What is Destrusor mucles?

Smooth muscle fibre mesh function as unit

What is Internal urethral sphincter?

Thickened smooth muscle at bladder neck

Where does female urethra exit?

External urtheral orifice between vagina and vestibule

How many parts does male urethra have?

Prostatic, pelvic, penile

What happens to prostate as age and what issues can it cause?

Enlarges with age

Benign prostatic hypertrophy (BPH) change micturition or obstruct rectum

What innervates external urethral sphincter/urethralis muscle?

S1-3 = small animals, S3-5 = large animals under voluntary control

Also innervate striated muscle in pelvic + perineal regions

What sympathetic motor innervation involved in micturition?

Preganglionic fibres from L1-4 synapse caudal mesenteric ganglia

Postganglionic fibres form hypogastric nerves to enter pelvic plexus on rectal wall

Provide adrenergic (to contract) innervation to detrusor muscle (beta-2 receptors) and internal urethral sphincter (alpha-1 receptors)

What parasympathetic motor innervation involved in micturition?

Preganglion fibres form sacral spinal cord form pelvic nerves to enter pelvic plexus on rectal wall

Post-ganglionic nerves provide cholinergic (to relax) innervation to detrusor muscle

What provides bladder sensory innervation?

Stretch receptors detect fullness, relay to pelvic nerves → sacral segment spinal cord

What provide urethra sensory innervation?

Afferents detect flow, distension and pain relayed to pudendal nerve to sacral segment of spinal cord

Where is the Micturition centre and function?

In pons

Respond to bladder stretch receptor sensory info

Coordinate urethralis muscle relax and detrusor muscle contract

Use cerebral cortex for voluntary control

How is urine stored in bladder?

Sympathetic control contract urethral sphincter (prevent leakage)

Internal sphincter use alpha-adrenergic stimulation to constrict bladder neck

Beta-adrenergic receptors relax detrusor muscle for low pressure to fill bladder

Inhibition of pelvic nerves by hypogastric nerves

How is the bladder emptied when reaching full?

Stretch receptor impulse → pelvic nerves → sacral spinal cord → micturition centre (pons)

Inhibition pudendal nerve relax urethralis muslce

Stimulate sacral parasympatheric neuron contract detrusor muscle which inhibit adrenergic to internal urethral sphincter, this coordination cause urination