Chapter 26 anatomy II
Explain the effect of sympathetic stimulation on the kidney and the GFR during rest, exercise, and shock
Norepinephrine secreting sympathetic neurons innervate the blood vessels of the kidneys, sympathetic stimulation constricts the small arteries and afferent arterioles, thereby decreasing renal blood flow and filtrate formation. In response to great stress/shock, the afferent arterioles greatly constrict. This lowers renal blood flow so severely that the blood supply to the kidney is inadequate to maintain normal kidney metabolism. Tissues may be damaged if this response lasts too long.
What is the functional unit of the kidney?
Nephrons
Name the parts of a nephron
1. A renal corpuscle 2. A proximal convoluted tubule in the cortex 3. A loop of Henle with sections in both the cortex and the medulla 4. A distal convoluted tubule in the cortex
What are all the filtration membrane structures?
1. Fenestrated glomerular capillaries 2. Basement membrane between the capillary wall and the visceral layer of the Bowman capsule 3. Podocytes of the visceral layer of the Bowman capsule
Describe the structure and location of the loop of Henle
After the proximal convoluted tubule; nearer the medulla Has a descending and ascending limb First part of the descending limb is similar in structure to the proximal convoluted tubule. The portion nearer the medulla becomes very thin near the bend. The lumen in the part narrows and an abrupt transition occurs from simple cuboidal to simple squamous. The ascending limb is first simple squamous then simple cuboidal as it gets thicker.
Name the substances that are moved by active and passive transport. In what part of the renal tubule does this movement take place?
Amino acids, K+, Cl-, glucose and most other solutes are transported into the tubule cells with Na+. Water enters and leaves the cell by osmosis. Glucose, amino acids, Na+, Cl-, and many other solutes leave the cells across the basal membrane by facilitated diffusion.
What substances are secreted?List the mechanisms by which these substances are transported.
Ammonia (by product of protein metabolism) is diffused into the lumen of the renal tubule H+, K+, penicillin, and paraminohippuric acid (PAH) are actively secreted by either active transport or antiport processes into the renal tubule.
What is renal blood flow
Amoun tof blood through the kidneys per minute; equals cardiac output (5600 mL/min) times the percentage (21%; renal fraction) of cardiac output that enters the kidneys Around 1176 mL blood/min
What is renal plasma flow
Amount of plasma flowing through the kidneys per minute; equals renal blood flow times percentage of the blood that is plasma. Because the hematocrit is the percentage of the blood that consists of formed elements, teh percentage of the blood that is plasma is 100 minus the hematocrit. Assuming a hematocrit of 45, the percentage of the blood that is plasma is 55%. Renal plasma flow is therefore 55% of renal blood flow. Around 650 mL blood/min
Describe the structure of the afferent and efferent arterioles and the juxtaglomerular apparatus.
An afferent arteriole supplies blood to the glomerulus for filtration. An efferent arteriole transports the filtered blood away from the glomerulus. ? Not sure on structure
What is capsular hydrostatic pressure
An inward pressure that opposes filtration. This pressure is due to the force of filtrate volume on the wall of the B. Capsule
Explain the differences between the descending limb and the ascending limb of the loop of Henle.
Ascending: transforms from cuboidal to simple squamous nearer its thin segment because of highly concentrated IF in medulla. The thin segment off the descending limb is highly permeable to water. Also moderately permeable to urea, Na+ and other ions.Because the thin segment is so permeable to water and somewhat to solutes, water leaves this portion of the tubule by osmosis and some solutes move into this portion of the loop. Thin segment of ascending loop is permeable to solutes, but impearmable to water. Therefore, although teh gradient encourages water to leave the lumen of the thin segment of the ascending limb, no additional water exists. The ascending loop is surround by IF that is less concentrated toward cortex. As filtrate flows through the thin segment of the limb, solutes diffuse into the interstitial fluid, making the filtrate less concentrated.
On what side of the renal tubule cell does active transport take place during reabsorption of materials?
Basal membrane of proximal convoluted tubule
What is the direction of movement in tubular secretion?
Can be active or passive. Blood to tubule ?
Describe the structure and location of the collecting duct and papillary duct
Collecting duct: where several distal tubules converge; simple cuboidal; larger in diameter than other segments of nephron; form much of the medullary rays and extend through teh medulla toward the tips of the renal pyramids
List the functions performed by the kidneys and briefly discuss each
Excretion- 21% of blood pumped out of the heart each minute is routed to the kidneys Regulation of blood volume and pressure- can control the amount of urine and its concentration; regulate blood volume and hence blood pressure Regulation of blood solute concentrations- the kidneys help regulate the concentration of primarily the major ions; regulate other solute concentrations Regulation of extracellular fluid pH- excrete variable amounts of H+ to help regulate the extracellular fluid acidity Stimulation of red blood cell synthesis- secrete erythropoietin Activation of vitamin D- control calcium blood levels by activating vitamin D
Explain the blood supply for the kidney
Figure 26.7
What is the function of the renal corpuscle?
Filtration
Explain the structure of the filtration membrane
Filtration slits are between teh cell processes of the podocytes of the visceral layer. A basement membrane lies sandwiched between the endothelial cells of the flomerular capillaries and the podocytes of the Bowman capsule. The filtration membrane, in all, consists of the capillary endothelial, the basement membrane, and the podocytes of the Bowman capsule.
Name the three general processes involved in producing urine.
Filtration:BP in glomerular capillaries forces fluid and small molecules out of the blood; not everything is filtered- only things that fit through fenestrae Tubular reabsorption: transport proteins in nephron move water and some filtered molecules from the filtrate back into the blood in the peritubular capillaries; so that they're not lost in urine Tubular secretion: some tubule cells transport additional solutes from teh blood into the filtrate. Some of these solutes may not have been filtered by the filtration membrane; "throw away" items
Describe the structure and location of the proximal convoluted tubule
First section of the renal tubule The wall of the proximal convoluted tubule is composed of simple cuboidal epithelium. The proximal convoluted tubule cells rest on a basement membrane, which forms the outer surface of the tubule. Has many microvilli
List the components of a renal corpuscle
Glomerulus Bowman capsule
Where does tubular secretion take place?
In the blood? It's the movement of non filtered susbtances from the blood to the filtrate. Includes toxic by products of metabolism and drugs or molecules not normally produced by the body.
Describe what happens to most of the filtrate that enters the renal tubule.
Inorganic salts, organic molecules, and about 99% of the filtrate volume leave the renal tubule and enter the interstitial fluid. Because the pressure is low in the peritubular capillaries, these substances enter the peritubular capillaries and flow through the renal veins to enter the general circulation
Describe blood colloid osmotic pressure
Inward pressure that opposes filtration. It is due to the osmotic pressure of plasma proteins in the glomerular capillaries. The presence of these proteins draws fluid back into the glomerular capillary than at its beginning because there is a higher protein concentration at the end of the glomerulus.
Describe the structure of the glomerulus
It is a network of permeable capillaries. The glomerular capillaries have fenestrae.
What is the function of the juxtaglomerular apparatus?
It is located next to the glomerulus and consists of a unique set of afferent arteriole cells and specialized cells in tehe distal convoluted cells that are in close contact with each other. It secretes renin which plays an important role in the regulation of filtration formation and BP
What is the direction of movement of substances in tubular reabsorption?
It is the return of water and solutes in teh filtrate to the blood. The filtrate leaves the lumen of the Bowman capsule and flows through the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule and then into the collecting ducts.
Distinguish between cortical and juxtamedullary nephrons
Juxta: have renal corpuscles that are found near the medulla. They have long loops of Henle, which extend deep into the medulla. 15% of nephrons Cortical: have renal corpuscles that are distributed throughout the cortex. Their loops of Henle are shorter than those of juxta nephrons and are closer to the outer edge of the cortex
What are the two types of nephrons?
Juxtamedullary neprhones and the cortical nephrons
Describe the location, size, and shape of the kidneys
Kidneys are bean shaped located amongst the retroperitoneal organs (behind the visceral peritoneum); located on each side of the vertebral column near the psoas major muscles; t12-L3; about 11 cm long and wear about 130 g
Name the organs that make up the urinary system
Kidneys; ureter, urinary bladder, urethra
Describe the filtration membrane. What substances do not pass through it?
Located in renal corpuscle in the renal cortex. The filtration membrane allows water and small molecules to leave the blood while preventing blood cells and most proteins from leaving the blood. Only components smaller than 7 mm in size can pass through (size of fenestrae); although filtrate may appear to be plasma free since most proteins are larger than 7 mm, albumin is just slightly smaller than 7 which allows some for it to pass through. Therefore, filtrate contains 0.03% protein.
Describe autoregulation
Maintenance of a relatively constant glomerular filtration rate despite relatively large changes in blood pressure; maintenance of a relatively constant glomerular filtrate rate despite relatively large changes in blood pressure. This is maintained by myogenic and tubulogloerular feedback mechanisms
Describe the structure and location of the distal convoluted tubule
Not as long as the the proximal convoluted tubules Simple cuboidal, but cells are smaller than the cells of the proximal tubules Do not posses large number of microvilli
What is filtration pressure?
Pressure gradient that forces fluid from the glomerular capillary through the filtration membrane in to Bowman's capsule; glomerular capillary pressure minus glomerular capsule pressureminus colloid osmotic pressure
How does ADH affect reabsorption in the distal convoluted tubule?
Reabsorption of water is via osmosis across the wall of the distal convoluted tubule and the collecting duct when ADH is present. The interstitial fluid surrounding the distal tubule and collecting duct is more concentrated than the filtrate, so the water moves toward the high solute concentration area. In these conditions, a small volume of concentrated urine is produced. ADH causes the tubule wall to become more permeable to water. When ADH is absent, the distal convoluted tubule and collecting duct are not permeable to water and water stays in the filtrate and more urine is excreted.
Contrast the rates of renal blood flow, renal plasma flow, and glomerular filtration. How do they affect urine production?
Renal blood is 1176 mL per minute Renal plasma flow is 650 mL per minute Glomerular filtration is 125 mL per minute About 99% of the filtrate volume is reabsorbed into the blood as it travels through the renal tubule, and less than 1% becomes urine
What is the glomerular filtration rate
The amount of plasma (filtrate) that enters the Bowman capsule per minute; equals renal plasma flow times the percentage (19% filtration fraction) of the plasma that enters the renal capsule About 125 mL filtrate/min
List the structures found at the hilum and in the renal sinus of a kidney
The hilum is a small area on the concave, medial side of the kidney that is continuous with an adipose and connective tissue-filled cavity called the renal sinus. The hilum structures are the renal artery and nerves, which enter the kidney and the renal vein and ureter, which exit the kidney.
What is renal fraction?
The percentage of cardiac output that flows through the kidneys; average is 21%
Describe the renal capsule and the structures that surround the kidney
The renal capsule surrounds the kidney and is made of connective tissue; surrounding the capsule is a thick layer of adipose tissue, which cushions and protects the kidneys. Renal fascia surrounds the adipose tissue and helps anchor the kidneys to the abdominal wall. This is also covered by adipose tissue.
Describe a brief process of how urine is made and excreted.
The renal pyramids in the medulla of kidneys are a collection of tubes and ducts that transport fluid throughout the kidney and modify it into urine. Once urine is formed, ducts in the renal pyramids transport it toward the renal sinus. The tips of the pyramids, the renal papillae, point toward the renal sinus. In the renal sinus, another set of tubes collects the urine for movement to the bladder. When urine leaves a renal papilla , it empties into a small funnel shaped chamber surrounding the tip of the papilla called a minor calyx. Urine from many minor calyces drain into a major calyx. Eventually emptying into the renal pelvis, down a ureter to the bladder.
Describe how symport works in the renal tubule.
The symport of molecules and ions across the epithelial lining of the proximal convoluted tubule depends on the active transport of Na+, in exchange for K+ across the basal membrane. Symport is the process by which carrier proteins move molecules or ions with Na+ across the apical membrane. The Na+ concentration gradient provides the energy for symport.
Describe the structure of the Bowman capsule
There is a parietal layer and a visceral layer. The parietal layer is constructed of simple squamous epithelial cells. The epithelial cells become cubed at the beginning of the proximal convoluted tubule. The visceral layer is constructed of podocytes, which wrap around the glomerular capillaries.
How do the basement membrane and the podocytes contribute to filtration?
They contain negatively charged glycoproteins, which repel negatively charged plasma proteins and prevent them from exiting the blood.
How does glomerular capillary pressure affect filtration pressure and the amount of urine produced?
This is an outward pressure from blood pressing on the capillary walls. Basically just BP. The GCP forces fluid and solutes out of the blood into the B. Capsule. This GCP is higher than other capillaries because its diameter is smaller (efferent arteriole smaller than afferent arteriole and glomerular capillaries). Because the efferent is smaller in diameter, the BP is higher in this portion, which forces filtrate across the filtration membrane into the lumen of the B. Capsule.
What substances become increasingly more concetrated in the filtrate?
Urea, irate ions, creatine, sulfate, phosphates, and nitrates are reabsorbed but not to the same extent as water. They therefore become more concentrated in the filtrate as the volume of the filtrate become smaller. Excretion of these substances helps maintain homeostasis since theyre toxic
What are long loops of Henle adapted for?
Water conservation
Explain the myogenic mechanism
When blood pressure goes up, the smooth muscle in the wall of the afferent arteriole stretches. In direct response to stretch, the smooth muscle contracts, which constricts the afferent arteriole. (Low BP - less stretch receptor activity- arteriole dilates). In this way, blood supply to the glomerulus, and thus GFR, fluctuates very little even when arterial pressure changes
Where does urine production first begin?
When the filtration membrane filters the blood. The filtered fluid then enters the lumen inside the Bowman capsule.