Urinary Chapter Flashcards
(37 cards)
What is a nephron?
It is the structural and functional unit of the kidney
What is the structure of the nephron?
1) glomerulus
2) glomerular capsule:
3) proximal convoluted tubule
4) nephron loop
5) distal convoluted tubule
6) collecting duct
What is the glomerulus?
The blood supply which forms the filtrate, enters as the afferent arteriole and exits as the efferent arteriole which is narrower creating a pressure for better diffusion of the material to the glomerular capsule
What is the glomerular capsule?
Parietal layer made of simple squamous epithelium, visceral layer has podocyte which is responsible for the diffusion of the solutes through the fenestrated capillaries between its foot
How is the urine formed?
1) Filtration (in the glomerulus)
2) Reabsorption (in the tubules)
3) Active secretion (peristalsis)
What is filtration?
It is a nonselective passive process, depending mainly on the blood pressure, forcing water & solutes which are smaller than proteins through the capillary walls
What is the glomerular filtration rate?
- The volume of filtrate formed each minute by the combined activity of the 2 million glomeruli in the kidney, it is directly proportional to the NFP (combination of HPgc, HPcs, OPgs), total surface area available for filtration, filtration membrane permeability
How is the glomeruli filtration rate regulated?
1) Intrinsic control (Renal auto regulation, Maintains GFR in spite of changes in blood pressure “within the normal range of BP”):
- Myogenic (contraction and dialation of the smooth muscles, which stretches the walls off the afferent arterioles)
- Tubuloglomerular feedback (communication between the tubule & the glomerulus, the low NaCl in the ascending limb will act on the macula densa cells on the juxtaglomerular complex of the kidney inhibiting the release of vasoactive chemicals which will vasodialate the afferent arteriorle)
2) Extrinsic control (Maintains systemic blood pressure “outside the normal values”):
- Hormonal (renin-angiotensin-aldosterone, the inhibited vasoactive cells will act on the granular cells of the juxtaglomerular complex which will release renin releasing angiotensin II, increasing the aldosterone levels which will increasing Na+ reabsorption increasing the blood volume, and it will also constricts the arterioles increasing the systemic BP)
- Neural (Baroreceptors reflex via sympathetic nervous system, acts on the granular cells and a vasoconstrictor)
What is reabsorption?
- Its is mainly an active process, reabsorbing some water, glucose, amino acids, & ions
- Occurs mainly inn the proximal convoluted tubule, which are the most active reabsorbers (they absorbs all glucose and amino acids, 65% of Na+ & H2O)
- The bulk of electrolytes are reabsorbed by the time they reach the loop of henle
- Uric acid and urea are secreted into the filtrate
- The rest of the water is reclaimed in the descending limp of the loop of henle
- Solutes (Na+, K+, Cl-) are reabsorbed at the ascending limb off the loop of henle this will make the kidney control the concentration of the urine
- ADH regulates the reabsorption of water, and increase urea reabsorption from the collecting ducts
- Aldosterone is response for reabsorbing Na+ which is coupled by the K+ secretion into the collecting ducts, mainly due to low BP, Blood volume or hyperkalemia
- On the other hand ANP (atrial natriuretic peptide) released by the cardiac cells when the BV or BP is high, inhibits the reabsorption of Na+ at the collecting ducts which will decrease the BV & BP
- The parathyroid hormone (PTH) acts at the DCT, increasing he reabsorption of Ca2+
What is secretion?
The movement of materials from the Peritubular capillaries to the renal tubules (H+, K+, creatinine, drugs, urea, uric acid)
What is the proximal convoluted tubule
What is the loop of henle
Due to the difference in the locations where water is reabsorbed an electrolytes it plays a vital role in urine concentration
What are the chronic renal disease?
- Develops silently over the years
- GFR is less than 60ml/min for at least 6 months
- Filtrate formation decreases gradually, nitrogenous waste accumulates in the blood, blood PH drifts to acidic ranges
Mainly due to:
- Diabetes mellitus (44%)
- Hypertension (28%)
Other factors:
- Repeated kidney infection
- Heavy metal poisoning
- Physical trauma
What is renal failure?
- When the GFR is less than 15ml/min
- Clinical sign can be uremia, fatigue, anorexia, nausea, mental changes, & muscle cramps
Treatment options:
- Hemodialysis
- Kidney transplant
What is meant by hemodialysis?
- Artificial kidney
- Passes the patients blood through a tube that is permeable to selected substances
- Nitrogenous wastes & K+ which are present in the blood but not the in the bath will diffuse out of the blood
- Buffers are added to the blood (like H+ and glucose), which moves from the bathing solution to the blood
What are the characteristics of urine used in medical diagnosis?
- Yellow colored due to urochrome pigment from the destruction of RBC
- Sterile
- slightly aromatic
- pH 6
What are the abnormal urine constituents?
- Glucose (glycosuria “diabetes mellitus or nonpathological”)
- Proteins (Proteinuria/albuminuria “nonpathological or glomerulonephritis, hypertension”)
- Pus “WBC & Bacteria” (pyuria “urinary tract infection”)
- RBCs (Hematouria “bleeding of the urinary tract”)
- Hemoglobin (Hemoglobinuria “transfusion reaction, hemolytic anemia, etc”)
- Bile pigment (Bilirubinuria “liver disease”)
What are the ureters?
- Tubes that attaches the kidney to the bladder, which are continuous with the renal pelvis entering at the posterior aspect of the urinary bladder
- behind the peritoneum
- moves urine via gravity and peristalsis
- Its walls are formed of 3 layers:
1) The mucosa: Transitional epithelium which is continuous with the renal pelvis and the urinary bladder
2) the muscularis: smooth muscle sheets (internal longitudinal & external circular, there is a third muscular layer the “external longitudinal” which only appears at the lower third art)
3) the adventitia: fibrous connective tissue which covers the external surfacce
what is the urinary bladder?
- Smooth collapsible muscular sac
- Temporarily store of urine
- Rouge mucosa allows the dissension of the urinary bladder
- Trigone triangular between the three opening (two from the ureters and the urethral opening)
The layers are:
1) mucosa: made of transitional epithelium
2) three layers of muscles (detrusor muscle)
3) adventitia
- walls are thick and folded in a empty urinary bladder, it can expand significantly without increasing the internal pressure
- It can hold 500ml normally but it can hold more than 1000ml
How can we see the urinary bladder and ureters
Using a pyelogram, which is a special X-ray via injecting a dye filling the urinary bladder
What is the urethra?
- Thin walled tube that carries urine from the urinary bladder to the outside of the body, controlled by (internal sphincter muscles “not voluntary, sympathetic & parasympathetic” & the external sphincter muscles “voluntary, somatic nerves”
- 3/4cm in females and 20 cm in males where it carries the sperm and the urine
What is thee process of micturating (voiding)?
- Both sphincter muscles should be relaxed
- point micturition centre and afferent impulses from stretch receptors will:
- relax the Internal sphincter muscle as the urinary bladder is stretched, which is activated from impulses sent to the spinal cord and then back via the pelvic splanchnic nerves via activating the parasympathetic activity and deactivating the sympathetic activity
- External urethral sphincter must be relaxed voluntarily via decreasing the somatic motor nerve activity
- Holding the urine decreases the parasympathetic activity, and activates the sympathetic and somatic motor nerve activity via the point storage centre
What is meant by incontinence?
It is the inability to voluntarily control the external sphincter muscles, normal in children below 2 years, in adults it is usually due to pressure (pregnancy), emotional problems, etc
What is urine retention?
- Opposite to incontinence
- The bladder is unable to expel the urine like after a surgery where the urinary bladder is usually anesthetized requiring a little bit of time for the smooth muscle to regain its activity
- Can be due to benign prostatic hyperplasia which surround the neck of the urinary bladder
- Treated via introducing a catheter which drains the urine, preventing bladder trauma from extensive streching
