Functions of the juxtaglomerular apparatus and hormonal control in the urinary system

1. Functions of the
juxtaglomerular
apparatus and
hormonal control in
the urinary system

2. Objectives…
→ Characterization of the Juxtaglomerular
apparatus;
→ Hypothalamus-Pituitary System;
→ Neurohypophysis role in the regulation
and renal functions;
→ Adrenal glands and their production of
aldosterone;
→ Aldosterone and the Renin-Angiotensin
System;
→Water and Potassium regulation.

3. An introduction to the
juxtaglomerular apparatus …
• The initial, straight part of the distal tubule makes
contact with the vascular pole of the renal corpuscle of
its parent nephron and forms part of a specialized
structure, the juxtaglomerular apparatus (JGA)
LOCATION OF
JUXTAGLOMERULAR
APPARATUS
http://withfriendship.com/user/neeraj/juxtaglomerular_apparatus.php

4. An introduction to the
juxtaglomerular apparatus …
http://apbrwww5.apsu.edu/thompsonj/Anatomy%20&%20Physiology/2020/2020%20Exam%20Reviews/Exam%204/CH25%20Nephron%20III%20-%20Blood%20Supply%20&JGA.htm

5. Constitution of the
Juxtaglomerular Apparatus
Juxtaglomerular
Apparatus
Juxtaglomerular
Cells
Secretion of the
renin hormone
Macula Densa
Sensitive to the
concentration of
NaCl

6. Constitution of the Juxtaglomerular
Apparatus
• JGA forms at the point of contact between a nephron's distal tubule (D) and the
vascular pole of its glomerulus (G).
• At that point cells of the distal tubule become columnar as a thickened region
called the macula densa (MD).

7. Constitution of the Juxtaglomerular
Apparatus
• Smooth muscle cells of the afferent arteriole's (AA) tunica media are converted
from a contractile to a secretory morphology as juxtaglomerular granule cells (JG).
• Also present are lacis cells (L), which are extraglomerular mesangial cells adjacent
to the macula densa, the afferent arteriole, and the efferent arteriole (EA).

8. Constitution of the Juxtaglomerular
Apparatus
• A plastic section through an afferent
arteriole of a JGA shows the JG cells
(arrowheads) with secretory granules
containing renin.
• Activities of the macula densa and
renin released by JG cells produce an
incompletely understood
autoregulatory tubuloglomerular
feedback loop:
- To control arterial blood pressure,
- To maintain a relatively constant rate
of glomerular filtration despite
changes in blood pressure.

9. Hypothalamus-Pituitary System
• The pituitary gland is composed of an anterior part and a posterior part,
directly attached to the hypothalamus region of the brain by a stalk called the
infundibulum.
• The gland occupies a fossa of the sphenoid bone called the sella turcica .

10. Hypothalamus-Pituitary System
The hypothalamo-hypophyseal portal system and hormone release
in the pituitary.

11. Posterior Pituitary
Oxytocin ADH
- Uterine
contractions;
- Lactation.
- Stimulates
water
retention;
- Raises blood
pressure by
contracting
arterioles;
- Induces male
aggression.

12. Posterior Pituitary
Pars Nervosa
• Modified neural tissues containing
unmyelinated axons supported and
ensheathed by glia cells - pituicytes
(P);
• The axons run from the supraoptic
and paraventricular hypothalamic
nuclei and have swellings called
neurosecretory (Herring) bodies
(NB)
- from which oxytocin and
vasopressin are released upon
neural stimulation.
• The released hormones are picked
up by capillaries (C) for distribution
throughout the body.

13. Adrenal Glands
http://academic.kellogg.cc.mi.us/herbrandsonc/bio201_mckinley/http://drmichaelroth.wordpress.com/tag/adrenals/ endocrine%20system.htm

14. Aldosterone and the
Renin-Angiotensin System
http://antranik.org/the-renin-angiotensin-aldosterone-reflex/

15. Aldosterone and the
Renin-Angiotensin System
Decreased arterial
pressure
Increased
stimulation of the
JGA
JG cells secrete renin
into the blood
Renin cleaves the
plasma protein
angiotensinogen
Inactive decapeptide
angiotensin I is
formed
Angiotensin converting
enzyme (ACE) on lung
capillaries clips this to
angiotensin II
Angiotensin II raises
systemic blood
pressure
Angiotensin II
stimulates the adrenals
to secrete aldosterone
Aldosterone promotes
Na+ and water
reabsorption in the
distal tubules
Increase blood
pressure

16. Water Regulation by the ADH
• Sometimes the body has too little water and needs to
conserve it and too much water and needs to get rid of it.
• Most of the control of water takes place in the distal and
collecting tubules under control of ADH released by the
posterior pituitary under control of the hypothalamus in the
mid-brain area.

17. Water Regulation by the ADH
• ADH travels in the blood stream to the peritubular capillaries
and binds to receptors on the distal and collecting tubules
which causes water channels to open in the tubule walls.
• This allows water to diffuse through the tubule walls into the
interstitial fluid where it is collected by the peritubular
capillaries.

18. Water Regulation by the ADH
↓ Plasma Volume
↓ Venous, atrial and arterial
pressures
Posterior Pituitary
↑ Vasopressin Secretion
↑ Plasma Vasopressin
Collecting Ducts
↑ Tubular Permeability to H2O
↑ H2O Reabsorption
↓ H2O excretion
Excess H2O ingested
↓ Body-fluid osmolarity
(↑ H2O concentration)
↓ Firing by the hypothalamic
osmoreceptors
Posterior Pituitary
↓ Vasopressin Secretion
↓ Plasma Vasopressin
Collecting Ducts
↓ Tubular Permeability to H2O
↓ H2O Reabsorption
↑ H2O excretion

19. Water Regulation by the ADH
• Over 99% of the filtrate produced each day can be
reabsorbed.
• The amount of water reabsorbed from the filtrate back
into the blood depends on the water situation in the
body.
• When the body is dehydrated, most of the filtrate is
reabsorbed.

20. Relationship between
the two systems
http://www.quia.com/jg/1367589list.html

21. Relationship between
the two systems
• ADH and the RAAS are partners in homeostasis;
• ADH alone would lower blood Na+ concentration by
stimulating water reabsorption in the kidney, but the RAAS
helps maintain balance by stimulating Na+ reabsorption.
http://www.quia.com/jg/1367589list.html

22. Relationship between the two systems
• Both increase water reabsorption.
• The release of ADH is a response to an increase in the osmolarity of the blood.
• But, an excessive loss of both salt and body will reduce blood volume without
increasing osmolarity. This will induce a change the RAAS that responds to the fall
in blood volume and pressure by increasing water and Na+ reabsorption.
http://www.samsca.com/pathophysiology-heart-failure.aspx

23. Potassium Regulation
↓Plasma Volume
↑Plasma angiotensin II
↑Plasma Potassium
Adrenal Cortex
↑ Aldosterone secretion
↑ Plasma aldosterone
Cortical collecting ducts
↑ Sodium
Reabsorption
↑ Potassium
secretion
↓ Sodium excretion ↑ Potassium excretion

24. Thank you for
your attention
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