H.1 Hormonal Control
IB Assessment Statement
• H.1.1 State that hormones are chemical
messengers secreted by endocrine glands into
the blood and transported to specific target
cells.
Hormones are
Chemical messengers
• Produced in endocrine glands
• Travel through blood
• Affect the target tissues
IB Assessment Statement
• H.1.2 State that hormones can be steroids,
proteins, and tyrosine derivatives with on
example of each.
Hormone Examples
Steroid Hormones
Animation Steroid Hormone in action.
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/00724
37316/120109/bio46.swf::Mechanism%20of%20Steroid%20Hormone%20
Action
Peptide Hormone
Thyroxine Hormone Animation
• http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535
::535::/sites/dl/free/0072437316/120109/bio
47.swf::Mechanism%20of%20Thyroxine%20Ac
tion
IB Assessment Statement
• H.1.3 Distinguish between the mode of action
of steroid hormones and protein hormones
Steroid vs. Peptide Hormones
• Steroid hormone: (a) Pass straight
through the plasma
membrane
Directly affect the
expression of genes.
• Peptide hormone
• (b) Attachment to plasma membrane
receptor (
Glycoprotein) (c) Receptor-Hormone
complex (d) Stimulation of
secondary messenger in cytoplasm
which alters the action of the cell.
IB Assessment Statement
• H.1.4 Outline the relationship between the
hypothalamus and the pituitary gland
Hypothalamus and Pituitary
• The diagram shows the posterior
division of the forebrain; where the
hypothalamus connects the
cerebral hemispheres with the
middle portion of the brain.
• The hypothalamus has many
receptors for changes of internal
conditions and serves as a link
between the nervous system and
the endocrine system (pituitary).
• Below the hypothalamus is a
double lobed structure called the
pituitary that produces the
endocrine secretions when
stimulated by the hypothalamus.
Hypothalamus and Pituitary
The hypothalamus controls each lobe
of the pituitary slightly differently.
Control of Anterior Lobe
• Hormones are sent from the
hypothalamus to the anterior
pituitary via a blood vessel called
the portal vein.
• The hypothalamus acts as the
endocrine gland (a)
• Hormone travel in blood through
the blood vessel (portal vein)(b).
• The target tissue is the anterior lobe
of the pituitary(c). e.g. LH, TSH and
FSH
Hypothalamus and Pituitary
Control of Posterior Lobe of the
pituitary
• (d) Neuro-hormones are
synthesised in the hypothalamus
neuron. They are transported and
stored in vesicles in the axon
ending located in the posterior
pituitary.
• (e) Nerve impulses travel down the
axon into the posterior pituitary.
This causes the release of the
vesicles of hormones into the
blood stream at the posterior
pituitary. e.g. Oxytocin, ADH
IB Assessment Statement
• H.1.5 Explain the control of ADH secretion by
negative feed back
• H1.5 ADH and negative
feedback control
• This is an example of
control of the posterior
pituitary as outlines in
steps (d) and (e) above.
• This is an example of the
how the hypothalamus
and the posterior
pituitary integrate to
control the release of
another hormone.
• H1.5 ADH and negative
feedback control
• The homeostatic regulation of
water (osmoregulation) is
brought about by the action
of the hormone Anti-diuretic
hormone.
• The hypothalamus is sensitive
to changes in plasma
concentrations.
• Neurosecretory cells in the
hypothalamus synthesis ADH
and transport this along the
axon of their nerves for
storage in their synaptic knob
endings in the posterior lobe
of the hypothalamus.
• ..
• H1.5 ADH and negative feedback
control
• Osmoregulatory sensitive cells in
the hypothalamus which are
sensitive to plasma
concentrations stimulate the
neurosecretory cells to transmit
impulses to their storage regions
in the posterior lobe of the
hypothalamus.
• ADH is secreted and has its target
tissue of the Distal Convoluted
and Collecting tubules of the
kidney.
• The ADH causes the opening of
the Aquaporin (pores) which
increases water reabsorption
from kidney filtrate
Animation on how the kidney works
• http://www.sumanasinc.com/webcontent/ani
mations/content/kidney.html
• https://www.youtube.com/watch?v=ajgbnOB4jM
LE 44-14
Proximal tubule
NaCl Nutrients
HCO3–
K+
H2O
H+
NH3
Distal tubule
H2O
NaCl
K+
HCO3–
H+
CORTEX
Descending limb
of loop of
Henle
Filtrate
H2O
Salts (NaCl and others)
HCO3–
H+
Urea
Glucose; amino acids
Some drugs
Thick segment
of ascending
limb
NaCl
H2O
OUTER
MEDULLA
NaCl
Thin segment
of ascending
limb
Key
Collecting
duct
Urea
NaCl
Active transport
Passive transport
INNER
MEDULLA
H2O
The Kidney
• The kidneys regulate the
amount of water, salts and
other substances in the
blood.
• The kidneys are fist-sized,
bean shaped structures that
remove nitrogenous wastes
(urine) and excess salts
from the blood
• Because the kidney regulates
both salt and water
concentration in the blood it is
the central organ that controls
osmoregulation.
The urinary system: The pathway of
Urine to the outside the body.
• The ureters are tubes that carry urine from the
pelvis of the kidneys to the urinary bladder.
• The urinary bladder temporarily stores urine
until it is released from the body.
• The urethra is the tube that carries urine from the
urinary bladder to the outside of the body.
• The outer end of the urethra is controlled by a
circular muscle called a sphincter.
• These parts work together and are part of the
urinary system.
Blood vessels of the mammalian kidney
Each kidney is supplied with blood by a renal
artery and drained by a renal vein
Animation: Nephron Introduction
The Kidney
The kidney structure
Each kidney is composed of three sections:
1. The cortex is where the blood is filtered.
2. The medulla contains the collecting ducts
which carry filtrate (filtered substances) to the
pelvis.
3. The pelvis is a hollow cavity where urine
accumulates and drains into the ureter.
The Kidneys
Cortex
Medulla
Renal
artery
Renal vein
Ureter
To the bladder
Five Steps in the Formation of Urine
1. Ultrafiltration in the renal capsule
2. Selective reabsorption in the proximal
convoluted tubules
3. Water conservation in the loop of henle
4. Blood pH and ion concentration
regulation in the distal convoluted tubule
5. Water reabsorption in the collecting ducts.
Step 1: Ultrafiltration in the renul
capsule.
• Filtration occurs as blood pressure forces
fluid from the blood in the glomerulus into
the lumen of Bowman’s capsule
• This process is called Ultrafiltration
because it is powered by pressure of the
blood.
• The entire content of the blood is not
forced out.
• The basement membrane of the of the
capsule does not allow blood cells and
proteins to enter the filtrate.
Step 2 : Selective reabsorption in the
proximal convoluted tubules
• The convoluted proximal tubules is the
longest section of the nephron.
• The walls are one cell thick and they are
packed with mitochondria.
• The cell membrane in contact with the
filtrate is packed with microvilli to increase
surface area for absorption.
Step 2 : Selective reabsorption in the
proximal convoluted
• The proximal convoluted tubules absorb filtrate through the
following mechanisms:
– Movement of water via osmosis
– Active transport of glucose and amino acids across
membranes
– Movement of some minerals and ions via a
combination of active transport, facilitated diffusion
and some gas exchange of ions
– Diffusion of urea
– Movement of protein via pinocytosis (endocytosis)
Step 3 Water conservation in the loop of henle
figure 12.23 page 374
• The descending limb is permeable so
salt diffuses into the loop of Henle and
water diffuses out into the medulla
tissue.
• At the hairpin zone (base of the loop)
water and salt diffuse into the medulla
tissue.
• In the ascending limb of the loop of
Henle, salt diffuses from the permeable
loop tubule into the interstitial fluid of
the medulla, but water is retained
Step 4: Blood pH and ion concentration
regulation in the distal convoluted tubule
• The distal tubule cells are the same
as in the proximal tubule (one cell
thick, microvilli and lots of
Mitochondria)
• The role of the distal tubule cells is to
adjust the composition of the
blood, in particular pH.
• Blood pH is initially buffered by
blood proteins, but if it deviates from
a pH of 7.4 the concentrations of
Hydrogen ion (H+) and hydroxide
(OH-) are adjusted
• Blood pH does not vary outside the
range of pH 7.35 to 7.45, but urine
pH ranges from 4.5 to 8.2.
Step 5: Water reabsorption in the collecting ducts
• The collecting ducts are
where the water content is
regulated.
• When the water content of
the blood is low the
antidiuretic hormone (ADH)
is secreted from the
posterior pituitary gland.
• When the water is the blood
is high, NO ADH is
released.
.
Step 5: Water reabsorption in the collecting ducts.
• The permeability of the walls of the
collecting ducts are variable.
• If ADH is present the walls of the
collecting tubules become fully
permeable.
• This allows water to be withdrawn
from the filtrate of the tubule in the
medulla.
• The water will be taken up and
redistributed throughout the body.
• ADH is remove from the body by
the kidney
• When no ADH is present the walls
of the collecting duct become less
permeable.
LE 44-16a
Osmoreceptors
in hypothalamus
Thirst
Hypothalamus
Drinking reduces
blood osmolarity
to set point
ADH
Increased
permeability
Pituitary
gland
Distal
tubule
STIMULUS
The release of ADH is
triggered when osmoreceptor cells in the
hypothalamus detect an
increase in the osmolarity
of the blood
H2O reabsorption helps
prevent further
osmolarity
increase
Collecting duct
Homeostasis:
Blood osmolarity