TUBULAR SECRETION
description
Transcript of TUBULAR SECRETION
![Page 1: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/1.jpg)
1
TUBULAR SECRETION
Lecture-5Dr. Zahoor
![Page 2: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/2.jpg)
2
Objectives – Tubular SecretionDefine tubular secretionRole of tubular secretion in
maintaining K+ conc. Mechanisms of tubular secretion.
![Page 3: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/3.jpg)
3
• Three Basic Mechanisms (Renal Processes) Of Urine Formation include:1. Glomerular Filtration2. Tubular Reabsorption3. Tubular Secretion
URINE FORMATION
![Page 4: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/4.jpg)
4
TUBULAR SECRETION
Tubular Secretion is transfer of substances from the peritubular capillaries (capillaries surrounding the tubule) into the tubular lumen.
It helps to eliminate the compounds from the body
![Page 5: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/5.jpg)
5
Tubular Secretion
• First step is simple diffusion from peritubularcapillaries to interstitial fluid
• Entry from interstitial fluid to tubular cell can
be active or passive• Exit from tubular cell to lumen can be active or
passive• Examples: potassium, hydrogen, organic acids,
organic bases, NH3
![Page 6: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/6.jpg)
6
Calculation of Tubular Secretion
Secretion = Excretion - Filtration
H+, K+, NH3
Organic acids and bases
![Page 7: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/7.jpg)
7
Tubular Secretion
Tubular secretion is important for: Disposing of substances not already in the filtrate Eliminating undesirable substances such as urea and uric acid
Getting rid of excess potassium ions
Controlling blood pH by secreting H+
![Page 8: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/8.jpg)
8
TUBULAR SECRETION
The most important substances secreted are
- Hydrogen ion - Potassium ion - Para Amino Hippuric acid ( PAH) - Organic anion and cations - Drugs e.g. penicillin, aspirin,
Cemitidine - Hormones e.g. erythropoietin,
renin
![Page 9: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/9.jpg)
9
TUBULAR SECRETION
Hydrogen Ion Secretion: Hydrogen Ion Secretion is important in acid
base balance Hydrogen ion is secreted in the tubular lumen
and eliminated from the body in the urine H+ ion is secreted in proximal, distal, and
collecting tubule
We will discuss H+ ion secretion in detail with acid base balance.
![Page 10: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/10.jpg)
10
TUBULAR SECRETION
Potassium Ion Secretion: K+ ion secretion is controlled by
aldosterone 98% of K+ is intracellular (ICF – K =
140meq/l) ECF – K+ = 4meq/l Slight changes in ECF – K+ can affect
the membrane excitability, therefore, plasma K+ concentration is tightly controlled by the kidneys
![Page 11: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/11.jpg)
11
TUBULAR SECRETION OF K+
K+ is actively reabsorbed in PCT Na+ is actively reabsorbed and K+ is
actively secreted by principal cells in the distal and collecting tubules and controlled by Aldosterone.
Intercalated cells in DCT and CT actively secrete H+ and K+ ion
Intercalated cells work for acid base balance
![Page 12: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/12.jpg)
Potassium handling by nephron
![Page 13: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/13.jpg)
13
MECHANISM OF K+ SECRETION
K+ is secreted in the principal cell of DCT and CT. It is coupled to Na+ reabsorption by energy dependent basolateral Na+ - K+ pump
![Page 14: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/14.jpg)
14K+ ion secretion
![Page 15: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/15.jpg)
Principle cells in Late DCT & CT
![Page 16: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/16.jpg)
16
CONTROL OF K+ SECRETION
Most important control mechanism for K+ secretion is by aldosterone
Aldosterone causes Na+ reabsorption and K+ secretion by principal cells
Increased K+ concentration directly stimulates the adrenal cortex to increase aldosterone secretion
Decreased K+ concentration in plasma – causes decreased aldosterone secretion
NOTE – Aldosterone secretion by Na+ is through Renin-Angiotensin Aldosterone mechanism
![Page 17: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/17.jpg)
17
Control Of Aldosterone Secretion By K+ and Na+
![Page 18: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/18.jpg)
18
Sodium Reabsorption
![Page 19: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/19.jpg)
19
Mechanism of Aldosterone Action
Aldosterone : Aldosterone causes Na+ re absorption and K+ secretion
by principle cell
Aldosterone causes increased Na+ entry through luminal membrane into principal cells
Aldosterone causes Na+ pumping out of principal cells by Na+-K+ pump into interstial fluid at basolateral membrane
Aldosterone causes K+ entry into the cell by Na+ - K+ pump, it increases the concentration of K+ in the cell, which is driving force for K+ secretion (passively)
![Page 20: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/20.jpg)
20
Changes in Distal K+ Secretion Causes of
increased Distal K+ Secretion
- High K+ diet- Hyperaldosteronis
m- Alkalosis- Thiazide diuretics- Loop diuretics
Causes of decreased Distal K+ Secretion
- Low K+ diet- Hypoaldosteronism- Acidosis- K+ - sparing
diureticsNOTEHyperaldosteronism – Hypokalemia Hypoaldosteronism – Hyperkalemia
![Page 21: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/21.jpg)
21
EFFECT OF H+ SECRETION ON K+ SECRETION
During acid base regulation, intercalated cells in DCT secrete either K+ or H+
When there is acidosis, H+ ions secretion is increased and K+ secretion is decreased
This decreased secretion of K+ leads to K+ retention in the body fluids, therefore, in acidosis, there is hyperkalemia {increased K+}
![Page 22: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/22.jpg)
22
IMPORTANCE OF REGULATING PLASMA K+ CONCENTRATION
K+ plays important role in membrane potential
K+ changes in ECF, when there is increase or decrease in K+ level, it can affect the heart and can cause decreased cardiac excitability, decrease conduction, cardiac arrhythmia, fibrillation
K+ changes not only affects cardiac muscle but it also affects skeletal muscle and nerve conduction
![Page 23: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/23.jpg)
23
EFFECT OF DECREASED K+
Decreased K+ causes hyperpolarization, which decreases the excitability of the nerve
In Skeletal muscle, K+ depletion causes muscle weakness
K+ depletion causes abdominal distension due to smooth muscle dysfunction
![Page 24: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/24.jpg)
Organic Anion and Cation secretion
Proximal tubule contains two types of secretory carriers1. For organic anions2. For organic cations
Organic ions such as Prostaglandin, epinephrine – after their action removed from blood
Non filterable organic ions also removed Chemicals, food additives, non nutritive
substances Drugs – NSAID, antibiotics
![Page 25: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/25.jpg)
PAH –EXAMPLE OF SECRETION
PAH is an organic acid Used for measurement of renal plasma
flow Both filtered and secreted PAH transporters located in peritubular
membrane of proximal tubular cells.
![Page 26: TUBULAR SECRETION](https://reader035.fdocuments.in/reader035/viewer/2022081502/568165c4550346895dd8d08f/html5/thumbnails/26.jpg)
26
Thank you