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Urinary System Organs

Kidney – Filters blood, allowing toxins, metabolic wastes, and excess ions to leave the body in urine

Urinary bladder – provides a temporary storage reservoir for urine

Paired ureters – transport urine from the kidneys to the bladder

Urethra – transports urine from the bladder out of the body

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Urinary System Organs

Figure 25.1a

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Kidneys -Overview

Blood passes through kidney – filtration occurs at capillaries – 20% of plasma becomes filtrate

Filtrate passes through nephrons – water and electrolytes are reabsorbed

Some electrolytes, drugs and toxins may be secreted into filtrate by tubular secretion

= Urine

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Nephron

Tubular structures that produce filtrate from plasma

Water, electrolytes, drugs and toxins are removed or added to filtrate as filtrate flows through tubules

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The Nephron

Nephrons are the structural and functional units that form urine, consisting of:

Renal corpuscle

Glomerulus – a tuft of capillaries associated with a renal tubule

Glomerular (Bowman’s) capsule – blind, cup-shaped end of a renal tubule that completely surrounds the Glomerulus

Glomerular endothelium – fenestrated epithelium that allows solute-rich, virtually protein-free filtrate to pass from the blood into the glomerular capsule

04/19/23 Mickey Dufilho 6

Glomerular Filtration Rate (GFR)

Figure 25.9

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The Nephron

Figure 25.4b

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Renal Tubule

Proximal convoluted tubule (PCT) – composed of cuboidal cells with numerous microvilli and mitochondria

Reabsorbs water and solutes from filtrate and secretes substances into it

Reabsorbs 100% of glucose, amino acids, escaped proteins, some vitamins, 60-70% of Na+, K+, Cl-, Ca++ and water

Secretes H+, NH3 (ammonia), drugs, toxins, uric acid and histamine

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Renal Tubule

Loop of Henle – a hairpin-shaped loop of the renal tubule

Descending Limb

Impermeable to electrolytes, permeable to water

80% Water is absorbed, filtrate becomes hypertonic

Ascending Limb

Permeable to Na+ and Cl- but not water

Filtrate becomes hypotonic

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Renal Tubule

Distal convoluted tubule (DCT)

Reabsorbs:

Na+ directed by aldosterone

Water directed by ADH

Ca++ directed by PTH

Some HCO3-, depending on pH of blood

Secretes:

NH3, K+, drugs, toxins, and creatinine

Some H+, depending on pH of blood

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Collecting Tubule

Reabsorbs

Na+ directed by aldosterone

HCO3- depending on blood pH

Urea to maintain hypertonic interstitial fluid around nephron tubules

Water directed by ADH

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Afferent and Efferent Arterioles

Larger diameter vessel is incoming – afferent

Smaller diameter vessel is outgoing – efferent and it becomes the peritubular capillaries

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Capillary Beds of the Nephron

Every nephron has two capillary beds

Glomerulus

Peritubular capillaries

Each glomerulus is:

Fed by an afferent arteriole

Drained by an efferent arteriole

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Hemodialysis

Diffusion of solutes through semipermeable membrane

Dialysis machine- group of tubules that act like a nephron

Membrane allows free passage of glucose, electrolytes and nitrogenous wastes

Filtration and production of filtrate is not required