Urinary System Lecture 2

Nephron functional unit of the kidney

The Nephron Figure 25.4a, b

Parts of the nephron Parts of the nephron A normal kidney contains 800,000 to one million nephrons Renal corpuscle consists of Glomerulus – a tuft of capillaries associated with a renal tubule Bowman’s capsule (glomerular capsule) – a cup-like sac that houses the glomerulus

Renal Corpuscle Glomerulus inside Bowman’s capsule together called Renal Corpuscle

Renal Tubule PCT - Proximal convoluted tubule – reabsorbs water and solutes from filtrate & secretes substances into it Loop of Henle – part of the PCT that is hairpin shaped – reaches into medulla DCT - Distal convoluted tubule – functions more for secretion than reabsorption

Nephron types Cortical nephrons – 85% of nephrons located in the renal cortex Juxtamedullary nephrons – located at the cortex-medulla junction –Loops of Henle deeply invade the medulla –Extensive thin segments produce highly concentrated urine

Capillary Beds Figure 25.5a

Vasa recta After the efferent arterioles descend into the medulla they divide into long thin STRAIGHT capillaries called the vasa recta (Latin for straight vessels)

Urine formation The 3 big-picture processes Glomerular filtration – Tubular absorption + Tubular secretion = Excretion

Mechanisms of Urine Formation Urine formation and adjustment of blood composition involves three major processes –Glomerular filtration –Tubular reabsorption –Secretion Figure 25.8

Glomerular filtration Separates plasma fluid and small solutes from larger proteins and blood cells High blood pressure in glomerular capillaries forces fluid through capillary walls into Bowman’s capsule

Tubular reabsorption Returns filtered water and nearly all major nutrients to the blood Primary active transport of Na+ across cell membrane drives diffusion of Cl- and water; provides energy for reabsorption by secondary active transport or passive diffusion of other substances

Tubular secretion Removes harmful or excess substances from blood Substances move by active transport or passive diffusion from capillaries into the tubule

Filtrate contents = glomerular filtrate Contains all plasma components except protein Loses water, nutrients, and essential ions to become urine The urine contains metabolic wastes and unneeded substances

Countercurrent mechanism: Tubes that interact to make the excretory process work. Involves sodium pumps that create an area of high sodium concentration deep in the medulla, near the collecting duct This allows the kidneys to produce dilute or concentrated urine depending on your body’s needsThis allows the kidneys to produce dilute or concentrated urine depending on your body’s needs Interaction between the flow of filtrate through the loop of Henle (countercurrent multiplier) and the flow of blood through the vasa recta blood vessels (countercurrent exchanger) allow this process to work

Urinary infections UTIs Pyelitis - Acute inflammation of the pelvis of the kidney, caused by bacterial infection. –the renal pelvis, the central part of the kidney is where urine accumulates before discharge. –It is more common in women than in men.

Pyelonephritis pyelonephritis is when a urinary tract infection has reached the pyelum (pelvis) of the kidney Symptoms include: Loin pain, often severe Fever and shivers Blood-stained urine Foul-smelling and cloudy urine Painful and frequent urination Nausea and vomiting

Volume of blood filtered daily 200 liters! The kidneys filter the body’s entire plasma volume 60 times each day

Homeostatic (regulatory) Functions of the Kidney The kidneys help to maintain the fluid, electrolyte & pH of blood. –Monitored by hypothalamus (thirst determination)

aldosterone 3 hormones: aldosterone, antidiruetic hormone, & atrial natriuretic hormone work together to maintain blood volume & blood pressure. 1.Aldosterone-secreted by adrenal cortex to maintain Na+ & K+ balance (when aldosterone is released Na+ is reabsorbed into the blood).

ADH Antidiuretic 2. Antidiuretic hormone-ADH-released by posterior pituitary when solutes in blood are too concentrated due to lack of water intake once Na+ has been reabsorbed. Takes place in DCT` & collecting tubule & amount of urine decreases.

ANH Atrial natriuretic 3. Atrial natriuretic hormone-ANH-opposes actions of aldosterone & ADH / released by cardiac cells when atria of heart are overstretched due to HBP. Causes secretion on Na+=natriuresis. When Na+ is expelled so is water & blood volume & BP decrease.