Renal system

Cortical nephron

Short loop, mostly in cortex

Juxtamedullary nephron

Long loop, extends deep into medulla, important for concentrating urine

What nephron structures are in the cortex?

Renal corpuscle, PCT, and DCT

What nephron structures are in the medulla?

Deeper portions of loops of Henle and collecting ducts

What nephron structures are in both the medulla and cortex?

Collecting ducts

Urine formation=

filtration+reabsorption+ secretion

Excretion

Elimination of resulting urine

Filtration

Blood moves into the renal corpuscle and becomes filtrate

Reabsorption

The filtrate moves from the PCT to blood, recovers water, glucose, amino acid, and electrolytes

Tubular sectretion

PCT, DCT, and collecting ducts, from blood to filtrate, removes excess ions and wastes, helps regulate acid-base and electrolyte balance,

What is secreted into the PCT?

Waste/ drugs

What is secreted into the collecting duct?

H+ and K+

Tubular fluid past the collecting duct

Urine, removes substance from the body

Excretion

Filtration- reabsorption+ secretion

What part does the descending limb play in the medullary gradient?

Reabsorption of water

What part does the ascending limb play in the medullary gradient?

Na+ and Cl- reabsorption

Medullary gradient

An osmotic gradient that enables the kidney to concentrate urine

Renal corpuscle

Filtration, water and small solutes enter bowman’s space

PCT

Bulk reabsorption, reabsorbs most filtered water and electrolytes and almost all glucose and amino acids

Loop of Henle

Builds the osmotic gradient

DCT

Fine tunes Na+, K+, and H+ balance, regulated by aldosterone

Collecting duct

Final regulation of water and urine concentration, regulated by ADH

How is glucose handled in the kidney?

Filtered, mainly reabsorbed in the PCT, is not secreted, very little/none is excreted

How is Na+ handeled in the kidney?

Filtered, mostly reabsorbed, minimally secreted, small amount excreted

H+

Minimally filtered, not reabsorbed as free H+, secreted, excreted in urine

Creatinine

Filtered, minimally reabsorbed, some secretion, excreted in urine

What happens in the renal cortex?

Filtration (primary function), major site of bulk reabsorption, secretion in cortical tubules, holds renal corpuscle, PCT, and DCT

What happens in the renal medulla?

Reabsorption of water and solute (primary function), some secretion in collecting ducts, holds loop of Henle and collecting ducts, creates osmotic gradient, concentrates urine

Juxtaglomerular complex

In the DCT contacts the glomerulus, adjacent to the afferent arteriole, vital role in regulating blood pressure and electrolyte balance

Macula densa

In the juxtaglomerular complex, monitor and respond to the changes in NaCl concentration in the filtrate of the DCT

Juxtaglomerular cells

Releases renin, regulates BP, efferent arterioles dilate and constricts

How does the kidney effect erythropoesis?

A decrease in oxygen delivery leads to EPO release which increases erythropoiesis

NHE3 transporter

Na+/H+ exchange, in the PCT, antiporter, primary apical driver for filtereed sodium, Na+ from tubular lumen into the PCT cell, H+ out of cell into lumen

Na+/ glucose cotransporter 2

PCT, 90% filtered glucose, Na+ and glucose both out of tubular lumen into proximal tubular cell

Na+/K+ ATPase

In all renal tubule cells, primary electrogenic pump, 3 Na+ out of cell and 2K+ into cells per ATP

NBC1

Na+/HCO3- cotransporter, 8-% filtered bicarbonate, Na+ and HCO3- out of cell into blood

What factors affect glomerular filtration rate?

Glomerular blood hydrostatic pressure, Blood osmotic pressure, capsular hydrostatic pressure

Net filtration pressure=

GBHP- (CHP+BCOP)

Autoregulation

Local kidney control, myogenic and TGF

Hormonal reulation

RAAS

Autonomic regulation

Sympathetic NS, during a crisis

Myogenic regulation

Triggered by increase/decrease in blood pressure, afferent arteriole constricts/dilates, keeps GFR stable

TGF

Increase in NaCl delivery, afferent arteriole constricts, lowers GFR

What is the normal blood pressure of the afferent arteriole?

80-180 mmHG

RAAS regulation

Renin release triggered by a decrease in perfusion pressure or NaCl delivery/ increase in the sympathetic NS. Angiotensin 2 triggers efferent constriction, an increase in aldosterone, vasoconstriction, ADH, and thirst

Sympathetic NS regulation

Triggered by stress, pain, or hemorrhage, slows the kidney down, decreases renal blood flow, decreases glomerular hydrostatic pressure, decreases GFR, and activates the RAAS system. Maintains systemic blood pressure/ perfusion of the heart and brain

What are the age related changes in the kidney?

Decrease in number of functioning nephrons, decrease in GFR, decreased sensitivity to ADH, problems with micturition reflex (loss of muscle tone in sphincters)

Renal artery stenosis (RAS)

Main arteries leading to the kidneys narrow and reduce blood flow to kidneys. Can lead to hypertension, kidney failure, and cardiovascular disease

Atherosclerosis

Most common cause of RAS, plaques are build up of cholesterol, fatty substances, cellular waste products, calcium, and fibrin, narrow the lumen of the artery

Proteinuria

Protein in urine

Aldosterone

Increased Na+ reabsorption, increase in K+ secretion, secreted by the adrenal cortex, stimulated by low blood Na+ levels, increased K+ levels, and decreased blood pressure. Helps maintain blood volume and electrolyte balance

What can long term increased renal blood pressure/ flow cause?

Glomerulosclerosis, protein leakage, loss of kindey function

Osmolality

Concentration of dissolved particles in body fluid

What does a increase in plasma osmolality do?

Water will leave cells, thirst is stimulated, ADH is released

Goal of osmoregulation

Maintain water balance, osmolality, and circulating blood volumes,

ADH

Water balance, secreted by the posterior pituitary, stimulated when blood volume is decreased, blood becomes concentrated, increases water reabsorption, inserts water channels

What are the key hormones in fluid regulation?

Aldosterone, ADH, natriuretic peptides, and parathyroid hormone

Natriuretic peptides

Released by the heart

Parathyroid hormone

Ca2+ regulation

Sodium

Primarily regulated by aldosterone

Potassium

Influenced by aldosterone, excretion adjusted based on blood pH

Calcium

Regulated by parathyroid hormone and vitamin D

Phosphate

Regulated by PTH and vitamin D, linked to calcium regulation

Hypernatremia

High blood sodium levels, due to dehydration or excessive salt intake

Hyponatremia

Low blood sodium levels, caused by excessive water intake or medications

Vasopressin

ADH

Demopressin

ADH receptor agonist, increases water absorption by binding to V2 receptors to increase water channels and water permeability

What is a side effect of inhibiting ADH receptors?

Hyperkalemia

Why does concentration of potassium matter?

Controls resting membrane potential, cardiac rhythm and skeletal excitability, acid and base balance, intracellular osmosis

What moves K+ into cells?

Insulin, beta 2 agonists/ catecholamines, increase in pH

What removes k+ from the body?

Kidney excretion, an increase in aldosterone, GI binders or dialysis when needed

What ion movement does acidosis cause?

H+ into cells and K+ out

What ion movement does alkylosis cause?

H+ out of cells and K+ into cells

How is hyperkalemia treated?

Calcium, use insulin to move K+ into cells