Renal hemodynamics (blood flow and glomerular function) Flashcards
Describe the general structure of the urinary system
1) Kidney
2) Ureter
3) Bladder
4) Urethra
Describe the general anatomy of the kidneys
1) Capsule of the kidney
2) Renal cortex (outer partt)
3) Renal pyramids
4) Papilla (the end of the pyramid which filters into the calyx)
5) Nephron (inside the renal pyramids)
6) Renal medulla (in between the renal pyramids)
7) Minor calyx (gets the product of each pyramid “from the papilla”)
8) Major calyx (the union of 2/3 minor calyx)
9) Renal pelvis (union of the three major calyx), exits the kidney as the ureter
What is the function of the kidneys?
1) Excretion of urine
2) Excretion of waste products and foreign chemicals
3) Filtering blood plasma (60 times per day)
4) Reabsorbing water and glucose
5) Important site of gluconeogenesis (during starvation, from amino acids)
6) Secretion, metabolism, and excretion of hormones (like erythropoietin, activation of vitamin D)
7) Regulates the acid-base balance
8) Controls the arterial pressure
9) Regulates water and electrolyte excretion
- FYI: waste products like (urea, uric acid, creatinine, urobilinogen), foreign products like pesticides in food and toxins
How is the extracellular fluid regulated?
1) Glomerulus:
- Filtration (the first step of urine formation, as the blood goes to the glomerulus and gets filtered forming an “ultrafiltrate” in the bowman’s capsule)
- Provides the tubules with fluid so the volume and composition can get modified
2) Tubules (modifies the ultrafiltrate):
- Modifies the composition of the ECF by reabsorbing what is needed
- It secretes substances into the fluid
What is a nephron?
- Found in the pyramids of the kidney
- They are the functional unit of the kidney
- 1-1.2 million nephrons are found in each kidney
- They are made of two components (vascular component & tubular component)
- We have two types of nephrons (superficial cortical nephron “80%” and the juxtamedullary nephrons “20%”)
- Nephrons cannot be regenerated
- With age nephron decreases in number, however the kidneys has a strong adaptive ability
- The nephron has two sets of capillaries connected by the efferent arterioles (which makes the vascular system of the kidneys unique)
What is the vascular component of the nephron?
1) Glomerulus (capillary network formed from the afferent arterioles), which are surrounded by the bowman’s capsule/space
2) Afferent arteriole
3) Efferent arteriole
4) Peritubular capillaries
What are the tubular components of the nephron?
1) Bowman’s capsule (blood is ultra filtered in this space “first step in the formation of urine”)
2) Proximal tubule
3) Loop of henle
4) Distal tubule
5) Collecting duct
What parts of the tubular nephron lies in the cortex of the kidney?
1) Bowman’s capsule
2) Proximal tubule (continues to the medulla as the descending loop)
3) Macula densa
4) Distal tubule
5) Connecting tubule
6) Cortical collecting tubule
What are the tubular part of the nephron that are found in the medulla of the kidney?
1) Descending limb of the loop of Henle (continuation of the proximal tubule)
2) Thin segment of the ascending limb of the loop of Henle
3) Thick segment of the ascending limb of loop of Henle (continues as the macula densa and then the distal tubule)
4) Medullary collecting tubule
5) Collecting ducts
What are the different types of nephrons in the kidney?
1) Superficial cortical nephron (80% of the nephrons found)
2) Juxtamedullary nephrons (20% of the nephrons of the kidney)
Describe the superficial cortical nephrons
- They represent 80% of the kidneys nephrons
- They start and end in the cortex of the kidneys
- Their glomeruli is in the outer cortex, with hairpin loops that barely reaches the medulla
Describe the juxtamedullary nephrons
- They form 20% of all kidney nephrons
- Their glomeruli lies near to the corticomedullary border
- They have a long loop of Henle which descends deep into the inner medulla and papilla
- It is essential for the concentration of urine
Why is the juxtamedullary nephrons necessary?
For the concentration of urine when the body is in crisis
Describe the vasculature of the renal system?
1) Peritubular capillaries
- Found in the superficial cortical nephrons, and they supply nutrients to the epithelial cells
2) Vasa recta
- Peritubular capillaries that are found in the juxtamedullary nephrons, it is a long hairpin like following the loop of Henle
- Its function is to concentrate the urine
- FYI: these capillaries are arranged in series and they are connected by the efferent arteriole
Describe the structure of the juxtaglomerular apparatus
- They are specialized cells located in the distal convoluted tubule as it passes through the cortex in a fork fashion (as it gets surrounded by the afferent and efferent arterioles of the arterioles)
- In the DCT, the cells are called macula densa; on the other hand, in the walls of the arterioles, the cells are called the juxtaglomerular cells (together, these cells form the juxataglomerular apparatus)
What is the function of the juxtaglomerular apparatus?
- They sense the composition of the urine (mainly the sodium chloride) and respond to it accordingly
- They can also produce renin (when there is low sodium, low BP, and hypovolemia)
Describe the hemodynamics of a single nephron
- Starting in the glomerular capillaries (the filtering capillaries), they have high hydrostatic pressure (45mmHg) because the efferent arterioles are narrow and have a high resistance. This high pressure created will allow more blood to accumulate in the glomerular capillaries
- As the arterioles continue into the peritubular capillaries (the reabsorbing capillaries), there is a large drop in pressure from 45 to 7/8mmHg; here the low pressure allows reabsorption to occur
Describe the structure of the glomerulus
- Composed of capillary loops(glomerular capillary, “the vascular component”) that are invaginated into the bowman’s capsule (tubular component)
- The bowman’s capsule joins to the proximal tubule
What are the layers that must be breached by the blood for it to reach the bowman’s capsule (filtration apparatus)?
1) The endothelium of the BV
- Fenestrated (50-100nm)
2) The basement membrane of the BV
- It is negatively charged
3) The epithelium of the bowman’s capsule (podocytes)
- Contains filtration slits (30/40nm), selective porous membrane which is negatively charged
- AKA the filtration apparatus
What characteristic of the filtration barrier does not allow the blood cells to enter into the bowman’s capsule?
The fenestration of the capillary endothelium
What forms the basement membrane of the BV?
1) Lamina rara interna
2) Lamina densa
3) Lamina rara externa
- Made of a proteoglycan gel, and it is negatively charged
What substances can pass through the filtration barrier?
- Positivley charged (cations) that are not larger than the slits (50-100nm for the capillary endothelium and 30-40nm for the capsular epithelial cells “epithelial podocytes”)
What are the substances that are freely filtered into the bowman’s capsule?
1) Sodium
2) Chloride
3) Potassium
4) Crystalloids
5) Bicarbonate
6) Urea
7) Glucose
8) Aminoacids
9) Organic acids
10) Insulin
11) Hemoglobin
12) Myoglobin
13) Water
What are the substances that are not freely filtered into the bowman’s capsule?
1) Albumin
2) Plasma protein
3) Lipid-soluble substances that are attached to the protein
4) Bilirubin
5) T4 cells
6) Unbound lipid-soluble substances (like free cortisol)
7) Colloids
