anatomy 2020: chapter 25 urinary system

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Urinary system functions

adjust blood pH, blood volume and BP, regulate electrolytes, conserve nutrients, remove drugs & toxins

kidneys

produce urine, functional unit is the nephron

ureters

lined with transitional epithelium, transport urine to bladder

bladder

lined with transitional epithelium, surrounded by detrusor muscle, stores urine

urethra

transports urine out of the body, shared with the reproductive system in male bodies

nephron

lined with simple cuboidal epithelium, functional unit of the kidney, actual location of urine production

renal corpuscle

consists of glomerulus and Bowman's capsule, location of filtration

glomerulus

fenestrated capillary network in the renal corpuscle

Bowman's capsule

cup-shaped part of the nephron, surrounds glomerulus, includes parietal layer of simple squamous epithelium and visceral layer of podocytes

reabsorption

process by which water and dissolved substances are taken back into the blood

proximal convoluted tubule (PCT)

\>99% of nutrients, some electrolytes, and 60% obligatory water reabsorption from tubular fluid

ascending limb of loop of Henle

portion of nephron loop where sodium ion, chloride ion, and potassium ion are reabsorbed

nephron loop (loop of Henle)

establishes osmotic gradient for water reabsorption

descending limb of loop of Henle

portion of nephron loop where obligatory water reabsorption occurs

distal convoluted tubule (DCT)

secretion of toxins/drugs

facultative reabsorption of water can occur (controlled by ADH)

reabsorption of Na+ (Na+/K+ exchange pump controlled by Aldosterone OR Na+/H+ exchange pump stimulated by low pH)

afferent arteriole

transports blood INTO the glomerulus, larger diameter than efferent arteriole

efferent arteriole

transports blood OUT (exit) of the glomerulus, smaller diameter than afferent arteriole

peritubular capillaries

capillary network wrapped around the nephron

Juxtaglomular Apparatus (JGA)

endocrine cells located between afferent arteriole and DCT, release renin

macula densa

regulates fluid composition of DCT and flow rate, release ATP, adenosine, and renin

podocytes

visceral layer of glomerular capsule that wraps around glomerulus, form filtration slits

mesangial cells

located between vessels of the glomerulus, controls capillary diameter and thus blood flow

glomerular hydrostatic pressure (GHP)

drives filtration of water, nutrients, electrolytes, and waste out of the glomerulus, blood pressure is higher here than systemic blood pressure

blood colloid osmotic pressure (BCOP)

pressure created by the retention of albumin proteins in the blood, pulls some fluid back into the glomerulus

capsular hydrostatic pressure (CsHP)

pressure exerted by filtrate already present inside the glomerular capsule provides slight opposition to filtration

filtration pressure (FP)

actual pressure that causes filtration

glomerular filtration rate (GFR)

amount of filtrate produced each minute, regulated by local control (autoregulation), endocrine and neural responses

autoregulation of low GFR involves

dilation of afferent arterioles, constriction of efferent arterioles, and contraction of mesangial cells

central regulation of low GFR involves

activation of RAS

Renin-Angiotensin-Aldosterone System (RAS or RAAS)

renin \> angiotensin I \> (A.C.E) \> angiotensin II \> aldosterone, neural responses (ADH) \> increased systemic BP and glomerular hydrostatic pressure

renin

released by juxtaglomular complex when BP and GHP is low, triggers formation of angiotensin I

angiotensin I

formed in the blood when renin is released, is converted to angiotensin II by angiotensin converting enzyme (A.C.E)

angiotensin II

triggers neural responses (thirst, production ADH, increase sympathetic motor tone) and the release of aldosterone

aldosterone

released by adrenal cortex when angiotensin II is released, causes reabsorption of Na+ at the DCT

ADH

released by neurohypophysis when angiotensin II is released, causes facultative water reabsorption at the DCT and collecting tubule

pathway for formation and excretion of urine

glomerulus \> glomular capsule \> PCT \> loop of Henle \> DCT \> collecting duct \> papillary duct \> minor calyx \> major calyx \> renal pelvis \> ureter \> urinary bladder \> urethra

collecting ducts

facultative water reabsorption can occur (controlled by ADH), concentration of urea, fluid called urine

detrusor muscle

smooth muscle around the wall of the bladder, contracts during micturation reflex to increase pressure (part of positive feedback loop)

voluntary relaxation of external urethral sphincter

leads to relaxation of internal urethral sphincter

countercurrent multiplication

Involves filtrate flowing in opposite directions through limbs of the loop

aquaporin channels

channels in the cells of DCT and collecting duct that allow for rapid reabsorption of water, controlled by ADH