Biology 212 Anatomy & Physiology I Renal or Urinary System

Renal (Urinary) System Primary function: Maintains homeostasis by regulating concentrations of both water and solutes in the blood. Disposes of metabolic wastes excess water excess ions toxins while retaining proper amount of water proper concentrations of ions nutrients anything else needed in blood

Renal (Urinary) System Primary function: Maintains homeostasis by regulating concentrations of both water and solutes in the blood. Disposes of metabolic wastes excess water excess ions toxins while retaining proper amounts of water proper concentrations of ions nutrients anything else needed in blood Secondary function: Regulates blood pressure within normal range (homeostasis)

Organs of Renal System

Kidney Located high in abdominal cavity Posterior to peritoneum Liver pushes right kidney more inferiorly Mass ~ 150g Size ~ 12 cm x 6 cm x 3 cm

Kidney Located high in abdominal cavity Posterior to peritoneum Liver pushes right kidney more inferiorly Mass ~ 150g Size ~ 12 cm x 6 cm x 3 cm Lateral surface convex Medial surface concave with hilus where renal artery, renal vein, ureter connect

Kidney Capsule: External covering of dense irregular connective tissue Cortex: Outer solid region Medulla: Inner solid region 8 to 12 cone-shaped masses (apex toward hilus) called renal pyramids, separated by renal columns Pelvis: Hollow medial region, extensions = calyces Connects medially with ureter

Kidney: Each renal artery (direct branch of aorta) divides into lobar or segmental arteries, which divide into interlobar arteries, then arcuate arteries (between cortex & medulla), which give off interlobular arteries (Saladin calls these “cortical radiate arteries”) into the cortex.

In the cortex, interlobular arteries (called “cortical radiate” arteries in Saladin) send blood through afferent arterioles into groups of capillaries called glomeruli. This is where filtration will occur to begin formation of urine (more on that in a moment).

In the cortex, interlobular arteries (called “cortical radiate” arteries in Saladin) send blood through afferent arterioles into groups of capillaries called glomeruli. This is where filtration will occur to begin formation of urine (more on that in a moment). From a glomerulus, blood flows out an efferent arteriole to another set of capillaries called peritubular capillaries which surround the tubules (more in a moment) where urine is forming.

Each renal artery divides into lobar/segmental arteries, interlobar arteries, arcuate arteries, interlobular arteries, afferent arterioles, glomeruli, efferent arterioles, peritubular capillaries Blood then flows into interlobular veins or arcuate veins, interlobar veins, and lobar veins to reach the renal vein which carries it to the inferior vena cava.

Let’s go back to the glomerulus: Consists of a group of interconnected capillaries. As blood flows through these capillaries, plasma (the liquid part of blood) is filtered out and flows though a series of tubes to form urine. This series of tubes is called a nephron.

Distal Convoluted Tubule Glomerular (Bowman’s) Capsule Proximal Convoluted Tubule Collecting Duct Loop of Henle

Each kidney contains ~ 1,000,000 nephrons Pattern of nephrons creates pattern of cortex and medulla: Cortex consists primarily of convoluted tubules which twist many directions. Medulla consists primarily of loops of Henle & collecting ducts all oriented in the same direction

Functions of nephrons:

Thus: Primary function of renal system: Maintains homeostasis by regulating concentrations of both water and solutes in the blood. Disposes of metabolic wastes excess water excess ions toxins while retaining proper amount of water proper concentrations of ions nutrients anything else needed in blood

Two types of “pressure” are involved in these processes of filtration, reabsorption, and secretion. 1) Hydrostatic pressure = weight of water or blood pressure 2) Osmotic pressure caused by different concentrations of solutes on different sides of a membrane. This can cause movement of both solutes and water (please review diffusion and osmosis in Saladin Chapter 3)

Two types of “pressure” are involved in these processes of filtration, reabsorption, and secretion. 1) Hydrostatic pressure = weight of water or blood pressure 2) Osmotic pressure caused by different concentrations of solutes on different sides of a membrane. This can cause movement of both solutes and water A. Solutes diffuse from where they are in higher concentration to where they are in lower concentration

Two types of “pressure” are involved in these processes of filtration, reabsorption, and secretion. 1) Hydrostatic pressure = blood pressure 2) Osmotic pressure caused by different concentrations of solutes on different sides of a membrane. This can cause movement of both solutes and water B. Water moves from where solutes are in lower concentration to where they are in higher concentration until hydrostatic pressure = osmotic pressure

Filtration

Structure of Glomerulus

Structure of Glomerulus Capillary wall (simple squamous epithelium, fenestrated) plus podocytes plus basement membrane between them form the filtration membrane across which liquid is filtered from the blood to the glomerular capsule.

Filtration: a) Holes (“fenestra”) of capillary epithelium ~ 75 nm; stop anything larger than that but let smaller molecules pass through

Filtration: a) Holes (“fenestra”) of capillary epithelium ~ 75 nm; stop anything larger than that but let smaller molecules pass through b) Holes in basement membrane ~ 7 nm; stop anything larger than that

Filtration: a) Holes (“fenestra”) of capillary epithelium ~ 75 nm; stop anything larger than that but let smaller molecules pass through b) Holes in basement membrane ~ 7 nm; stop anything larger than that c) Spaces between podocytes (“filtration slits”) ~30 nm; Thus: only things smaller than ~ 7 nm can be filtered from blood into urine

Filtration: (Only things smaller than ~ 7 nm can be filtered from blood into urine) Not quite that simple, since electrical charge also affects what can pass through the filtration membrane.

All cells & molecules > 7 nm stay in blood Filtration: (Only things smaller than ~ 7 nm can be filtered from blood into urine) Not quite that simple, since electrical charge also affects what can pass through the filtration membrane. In general: All cells & molecules > 7 nm stay in blood Neutral molecules 3 - 7 nm pass through, but charged molecules (ions) this size can not All molecules & ions < 3 nm pass through Thus: Water Glucose Electrolytes Amino acids Fatty acids Vitamins Most metabolic wastes etc. are all filtered out of the blood

This fluid filtered out of the blood flows into the proximal convoluted tubule, through other parts of nephron, into collecting duct.

This fluid filtered out of the blood flows into the proximal convoluted tubule, through other parts of nephron, into collecting duct. Recall that nephron is surrounded by peritubular capillaries

As this filtrate passes through the nephron: a) Most solutes needed by body & most of the water are reabsorbed back into the blood in peritubular capillaries b) Excess solutes & excess water stay in urine c) Additional unwanted ions and molecules secreted into urine

Reabsorption from Nephron: Substance: Amount Amount Reabsorption filtered excreted ( % ) per day per day Water ( L ) 180 1.8 99 Sodium ( g ) 630 3.2 99.5 Glucose ( g ) 180 0 100 Urea ( g ) 54 30.0 44 (From Mader, Human Biology)

Key Feature of Kidney: Nephrons can concentrate urine by reabsorbing most of the water filtered out of the glomerulus Substance: Amount Amount Reabsorption filtered excreted ( % ) per day per day Water ( L ) 180 1.8 99 Sodium ( g ) 630 3.2 99.5 Glucose ( g ) 180 0 100 Urea ( g ) 54 30.0 44

Key Feature of Kidney: Nephrons can concentrate urine by reabsorbing most of the water filtered out of the glomerulus Substance: Amount Amount Reabsorption filtered excreted ( % ) per day per day Water ( L ) 180 1.8 99 Sodium ( g ) 630 3.2 99.5 Glucose ( g ) 180 0 100 Urea ( g ) 54 30.0 44 This requires kidney to create a large concentration gradient in extracellular fluid of medulla (surrounding loops of Henle)

Low osmolarity (concentration of solutes) closer to cortex Key Feature of Kidney: (Nephrons concentrate urine by reabsorbing most of the water filtered out of glomerulus. This requires kidney to create a large concentration gradient in extracellular fluid of medulla, surrounding loops of Henle) Low osmolarity (concentration of solutes) closer to cortex High osmolarity (concentration of solutes) deeper in medulla

Low osmolarity (concentration of solutes) closer to cortex Key Feature of Kidney: (Nephrons concentrate urine by reabsorbing most of the water filtered out of glomerulus. This requires kidney to create a large concentration gradient in extracellular fluid of medulla, surrounding loops of Henle) Low osmolarity (concentration of solutes) closer to cortex High osmolarity (concentration of solutes) deeper in medulla so that As newly formed urine passes through collecting, most of the water will diffuse out of collecting duct, into the extracellular fluid, from which it will diffuse back into blood of the peritubular capillaries, leaving high concentration of solutes in urine which reaches pelvis & leaves kidney

Your text goes into great detail about how this happens (including these diagrams): You don’t need to understand details, but you should understand that it allows the final urine to be concentrated by pulling water out of it as it passes through the collecting duct

Your text goes into great detail about how this happens (including these diagrams): You don’t need to understand details, but you should understand that it allows the final urine to be concentrated by pulling water out of it as it passes through the collecting duct. How much water gets pulled out can increase or decrease if body needs to retain or lose water. This is under control of antidiuretic hormone (ADH) produced by posterior pituitary.

Target cells for ADH: Epithelium forming the collecting ducts (How much water gets pulled out can increase or decrease if body needs to retain or lose water. This is under control of antidiuretic hormone (ADH) produced by posterior pituitary). Target cells for ADH: Epithelium forming the collecting ducts Increased reabsorption of water from urine back into blood Less urine, more concentrated Increase in ADH Decreased reabsorption of water from urine back into blood More urine, less concentrated Decrease in ADH

Kidney also has important function in regulating systemic blood pressure. Each nephron has a juxtaglomerular apparatus which detects pressure of blood in the afferent arteriole and secretes the hormone renin. The lower the blood pressure in the afferent arteriole, the more renin the juxtaglomerular apparatus will secrete.

(Each nephron has a juxtaglomerular apparatus which detects blood pressure in afferent arteriole and secretes hormone renin. The lower the blood pressure in the afferent arteriole, the more renin the juxtaglomerular apparatus will secrete.)

Urine passes from a collecting duct into a minor calyx, then a major calyx, then the pelvis of the kidney.

Urine leaving the pelvis enters the ureter, which carries it to the urinary bladder.

Ureters: Retroperitoneal. Pass anterior to common iliac arteries & veins.

Ureters: Retroperitoneal. Anterior to common iliac arteries & veins. Deliver urine to posterolateral parts of urinary bladder.

Ureter: Mucosa: Transitional epithelium Lamina Propria (loose C.T.) Muscularis: Thick wall of smooth muscle Adventitia: Dense irregular C.T.

Urinary Bladder: In pelvis, posterior to pubic bone Superior surface covered by peritoneum Female: Anterior to uterus/vagina Male: Anterior to rectum Superior to prostate

Urinary Bladder: Mucosa: Transitional epithelium Lamina propria Muscularis: Thick smooth muscle (“detrusor”) Adventitia (C.T.) covers most of bladder Serosa on its superior surface

Urinary Bladder: Urine leaving bladder enters urethra

Urination Reflex: 1. Stretch receptors in wall of bladder send signals to sacral spinal cord. 2. Parasympathetic neurons stimulate contraction of muscularis and relaxation of internal urethral sphincter.

Voluntary Control of Urination: Stretch receptors in wall of bladder also send signals to pons. 2. If urination isn’t convenient, somatic neurons stimulate contraction of external urethral sphincter to keep it closed. If urination is convenient, somatic neurons to the external urethral sphincter are inhibited to allow it to relax and open. Sympathetic neurons also relax the internal urethral sphincter and stimulate contraction of the muscularis of the bladder.

Urethra: Adventitia: Dense irregular C.T. Muscularis: Thick wall of smooth muscle Mucosa: Epithelium varies from transitional near bladder to stratified squamous at end Male urethra much longer, has middle region of stratified columnar. Female urethra does not. Lamina Propria (loose C.T.)

External Urethral Sphincter External Urethral Meatus

Urine not modified in ureter bladder urethra Thus: Urine leaving body through external urethral meatus unchanged since it left kidneys. Also: Bacteria & other organisms can travel through urethra into bladder (“cystisis”); much more common in shorter urethra of women. From bladder, organisms can travel through ureters into kidneys (“pyelonephritis”)

Later today: Hold your urine for an additional 20-30 minutes, until you really have to urinate, and feel the contractions of your urinary bladder. You should also feel the contraction of your external urethral sphincter. When you start urinating, feel the relaxation of your external urethral sphincter. Midflow, contract your external urethral sphincter to stop the flow of urine, then relax it to restart the flow of urine. Tonight: On yourself or another person, locate your kidneys, ureters, bladder, and urethra