Nephron     GA

	Bowman's capsule
	Proximal (convoluted) tubule
	Nephron loop (loop of Henle)
	Distal (convoluted) tubule

Renal tubule

	Nephron
	Collecting duct (shared by several different nephrons)

Renal corpuscle: Bowman's capsule and glomerulus     GA

	Glomerulus     GA  ANIM Ball-like network of capillaries     FIG Supplied by an afferent arteriole Drained by an efferent arteriole (which leads to a second network of capillaries after the glomerulus) Endothelial cells of capillary wall has fenestrations or pores (like White Castle hamburgers) Acts as a filter, keeping blood cells and proteins in blood and allowing water and small solutes to filter out of blood Mesangial cells = "support cells" between the capillaries
	Bowman's capsule     GA Surrounds glomerulus like a hollow cup Inner wall of capsule adheres to outer walls of glomerular capillaries     FIG Cells are spider-like cells called podocytes (lit. "foot cells") Podocytes have pedicels or "toes" that interlock like a zipper to form a filtration membrane with slits (filtration slits) Filtration slits are covered with a thin fibrous membrane (slit diaphragm) Acts as second layer of filter
	Filtration membrane Glomerular capillary wall Basement membrane Inner wall of Bowman's capsule

Proximal [convoluted] tubule

	Convoluted means it has a lot of twists and turns
	Proximal refers to the fact that it is close to the beginning of the nephron

Nephron loop (Loop of Henle)

	Hairpin turn of the nephron, dipping far down into the medulla (from the cortex, where most of the nephron is located)
	Has a descending limb followed by an ascending limb     GA The ascending limb has a thick-walled region

Distal [convoluted] tubule

Drains filtrate from the loop of Henle

Collecting tubule (duct)

	Drains filtrate from distal tubules of several different nephrons
	Many collecting ducts converge at the renal papillae and release urine from the kidney tissue

Blood supply: Afferent arteriole -> glomerulus -> efferent arteriole -> peritubular capillaries (includes vasa recta)

	Peritubular capillaries surround the entire nephron (except the Bowman's capsule, which has the glomerulus instead)
	Vasa recta (lit. "vessels at a right angle") conduct blood down, then up, the outside of the loop of Henle

Two types of nephron

	Cortical nephrons are further to the outside and have short nephron loops that do not reach into the medulla
	Juxtamedullary nephrons are mostly in the cortex close to the medulla and have long nephron loops that dip far into the medulla (from the cortex)

The basics--balancing of blood plasma & formation of urine     ANIM    ANIM [choose "Urinary" then "Urination"]

	Importance: adjusts fluid and electrolyte balance of blood (thus, entire body)
	Three essential functions: Filtration Reabsorption Secretion

Reabsorption and secretion

Reabsorption of most of Na⁺ , Cl^- and H₂O 

	Sodium is transported actively
	Chloride and water follow passively

Reabsorption of other solutes (passive - or actively cotransported with Na⁺)

Glucose transport maximum (Tmax) Co-transported with Na+ Na+ is pumped from back of tubule cell, drawing more Na+ in through front of tubule cell (by way of passive carriers) Carrier mechanism carry glucose at the same time Thus, the active-transport driven movement of Na+ brings glucose "along for the ride" Largest amount of glucose that can be transported at once Determined by how many passive carriers for glucose you have (the more carriers, the higher the transport maximum)

pH adjustment (H⁺ secretion)

About half of the urea is reabsorbed passively here

Creates/maintains osmotic gradient between medulla and cortex

Medulla's IF maintained at high saltiness

	"saltiness" is measured as osmolality (units: mOsm)
	high osmolality = high saltiness = high osmotic pressure (tendency to gain water by osmosis) = hypertonic
	Most body fluids are isotonic to each other at about 300 mOsm
	Medullary IF goes up to about 1200-1400 mOsm

Salt actively removed by ascending limb

This is the countercurrent multiplier mechanism A "countercurrent mechanism" simply implies that fluid is flowing in opposite directions right alongside each other (as does highway traffic)

Makes IF hypertonic (1200 mOsm)

	That is, IF has osmolality or high salt content
	Urea from collecting duct adds to high osmolality of IF

Also makes filtrate hypotonic (low osmolality) 100 mOsm

Vasa recta also has a countercurrent flow

This reduces removal of solutes from interstitium Compare to straight-line flow of blood, which would remove all the salt added to the IF by the loop of Henle This mechanism is called "countercurrent exchange"

Countercurrent multiplier mechanism in the loop of Henle

Increases saltiness of medullary IF (reduces saltiness of the filtrate)

Countercurrent exchange mechanism of the vasa recta     FIG

Reduces the rapid removal of salt from the medullary IF

Secretion and adjustment of final urine osmolality

ADH (antidiuretic hormone from posterior pituitary gland)

	Promotes tubule wall's H2O permeability
	H2O can diffuse out of tubule into hypertonic IF
	Adjusts final osmolality of urine You can now have a range of osmolality of urine from 100 mOsm (hypotonic) to 300 mOsm (isotonic) to 1200 mOsm (hypertonic) Depends on how much water the body needs to save (conserve) or get rid of to achieve balance (homeostasis)

Aldosterone (hormone from adrenal glands)

	Increases K+ secretion Thus, increases Na+ reabsorption (K+ is "traded" for Na+)
	Makes urea a more dominant solute Indirectly increases H2O reabsorption (permitted by ADH)
	Conserves plasma volume
	Renin-angiotensin mechanism (see figure in textbook for details) Involves renin from the juxtaglomerular (JG) cells at junction of distal tubule and afferent arteriole of the glomerulus

ANH (atrial natriuretic hormone from atrial walls of heart)

	Triggered by increase in blood plasma volume, which stretches the atrial wall beyond normal
	Increases Na+  loss by plasma This in turn causes osmosis of H2O out of blood and into the filtrate
	Loss of water from blood tends to lower plasma volume
	ANH opposes the action of aldosterone Allows for fine-tuning of water content of body

Water (about 95%)

Ions (mostly sodium and chloride, along with some others including H⁺)

Urochromes (pigments)

	Mostly bile pigments from breakdown of old RBCs in spleen, etc.
	Could be some beta-carotenes from food / supplements

Wastes

	Nitrogenous waste Urea = waste of breaking down amino acids so they can be used for cellular respiration (in place of glucose)
	Excess drugs, hormones, toxin

Blood plasma: 7.35 - 7.45

Changes as small as 0.1 pH unit can have profound effects on cellular functions

Acidosis

	pH 7.34 - 6.80
	Respiratory acidosis (if caused by respiratory mechanism)
	Metabolic acidosis (if caused by anything else)

Alkalosis

	pH 7.46 - 8.00
	Respiratory alkalosis (if caused by respiratory mechanism)
	Metabolic alkalosis (if caused by anything else)

Buffer mechanisms

	In blood plasma
	Several pairs of buffers Bicarbonate system Phosphate system protein (Hb) system
	Act to neutralize additions of acids or bases

Respiratory mechanism

	Hyperventilation: Decreases carbon dioxide (Pco2) Thus, raises pH
	Hypoventilation: Increases carbon dioxide (Pco2) Thus, lowers pH

Renal mechanisms

H+ secretion

Compensation

"Compensated acidosis" and "compensated alkalosis" refer to conditions where the body's mechanisms for balancing pH are attempting to maintain normal pH despite an abnormal disturbance to the usual pH scenario