Urinary System Physiology

Homeostatic functions

maintain water balance

regulate quantity and concentration of ECF ions

maintain proper plasma volume

assist in maintaining acid-base balance

maintain proper osmolarity of body fluids

excrete end products of bodily metabolism

excrete many foreign compounds

secrete erythropoietin

secrete renin

convert vitamin D (cholecalciferol) into an active form

diagram of kidney structure; section of human kidney

blood supply to the kidney; circulation in the renal cortex

Formation of urine by the kidney

functional anatomy of the kidney: the nephron

diagram of the nephron

vascular components

structure of the renal corpuscle

afferent arteriole

glomerulus ¹

efferent arteriole

peritubular capillaries

tubular components

Bowman’s capsule

proximal tubule

loop of Henle

distal tubule

collecting duct

basic nephron function

glomerular filtration

glomerular membrane

podocytes

mesangial cells

filtration slits

net filtration pressure

glomerular-capillary BP

blood-colloid osmotic pressure

Bowman’s capsule hydrostatic pressure

glomerular filtration rate (GFR) ²

regulation of GFR

myogenic response

tubuloglomerular feedback

macula densa

JG cells and renin production

reflex control

tubular reabsorption

transepithelial transport

cross luminal membrane of tubular cell

cytosol of tubular cell

basolateral membrane of tubular cell

diffuse through interstitial fluid

penetrate capillary wall

protein transcytosis

passive reabsorption

active reabsorption

Na⁺-K⁺ ATPase

aldosterone ³

renin ⁴ → angiotensinogen → angiotensin I →
(ACE) → angiotensin II

atrial natriuretic peptide (ANP)

loop diuretics and ACE inhibitors

glucose and amino acid Na⁺ cotransport

transport maximum (T_m)

filtered load = [in plasma] × GFR

renal threshold

chloride, water and urea

BUN (blood urea nitrogen) and uremia

tubular secretion

hydrogen ions

potassium

reabsorbed proximally

variably secreted distally

organic anions and cations

excretion

micturition

Acid-base balance

acids and bases

weak vs. strong

pH = - log₁₀[H⁺]

acidosis, < 7.35 [6.8]

alkalosis, > 7.45 [8.0]

carbonic acid: bicarbonate (H₂CO₃:HCO₃^-) buffer system

CO₂ + H₂O ↔ H₂CO₃ ↔ H⁺ + HCO₃^-

protein buffer system

hemoglobin buffer system

H⁺ + Hb ↔ HHb

phosphate buffer system

Na₂HPO₄ + H⁺ ↔ NaH₂PO₄ + Na⁺
NaH₂PO₄ + OH^- + Na⁺ ↔ Na₂HPO₄ + H₂O

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Questions for thought
1.		What is a nephron? Briefly describe its structure and function.
2.		Outline the steps involved in the production of urine.
3.		Describe the juxtaglomerular apparatus and its function.
4.		Describe the mechanism the kidneys use to influence blood pressure.
5.		Distinguish diabetes mellitus from diabetes insipidus. Include a description of the cause(s) of each and the mechanism(s) by which each is expressed.
6.		Explain the important differences between blood plasma and renal filtrate, and relate the differences to the structure of the filtration membrane.
7.		Explain how chemical buffer systems resist changes in pH. Give examples of the operation of at least two buffer systems in the body.

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