Introduction to endocrinology
Contents
- Hormones
- Receptors
- Signal transduction
- Homeostasis
Hormones
Definitie: “Chemical secreted by a (group of) cell(s) into the blood for transport to a distant
target, where it exerts its effect at low concentrations.”
There is some overlap with other signaling molecules that have a likewise function:
IGF (insuline-like growth factor) → Growth factor
CCK (cholecystokinin) → Neurotransmitter
EPO (erythropoietin) → Cytokine
The specialized organs that (solely) produce hormones are:
- Thyroid gland
- Adrenal gland
- Pituitary gland
- Pancreas
Other tissues that produce hormones are:
- Adipose tissue
- Intestines
- Kidneys
- Bones
Hormones regulate:
- Growth and development
- Metabolism
- Reproduction
- Internal environments
They’re also involved in:
- Homeostasis
- Reacting to physical and emotional stress
- Responses to the environment
,Four main receptor types:
1. Receptor channels → binding
opens channel
2. Receptor enzymes → binding
to a receptor enzyme
activates intracellular
enzyme
3. GPCR → binding to GPCR
opens ion channel
4. Integrin receptors → binding
to integrin receptors alters
cytoskeleton
GPCR’s
These are the most common type of receptors in the human body. There are more than 800
different types known. These snake-like structures span the lipid bilayer 7 times before being
coupled to a G protein. GPCR’s are important drug
targets (approx. 40%) and have two different signal
transduction routes:
1. Adenylyl cyclase → vormt ATP om tot drie
cAMP moleculen → Protein kinase A
2. Phospholipase C → heeft of DAG of
IP3 als second messengers:
- DAG → PKC → gefosforyleerd
proteïne → cel respons
- IP3 → calcium opslag open →
cel respons
Intracellular receptors
There are two types of intracellular receptors. Type I resides within the cytoplasm and is
activated there. Once activated, it moves to the nucleus. Type II resides within the nucleus
and waits to be activated.
Homeostasis
Homeostasis consists of different types of setpoints around which the body tries to maintain
its balance. There are fixed setpoints that include:
- calcium, glucose and pH levels
And there are variable setpoints that include:
- Body temperature
, - Ontogenesis (growth)
- Seasonal cycles (e.g. circadian, ovarian)
Digestion
Feedback loops
Positive feedback doesn’t lead to homeostasis, it shuts off
the feedback cycle and leads to critical transitions where
there’s no return. Example: whenever the head of a baby
touches the bottom of the uterus, the muscle cells will release
large amounts of oxytocin.
Metabolism
The body has a mass balance, in which the respiratory system plays a
major role. Every day an average of 9L (2L of food and drink, the rest of
the organs) of fluids enters the intestines. Only 0.1L goes out again.
The peritoneum is the serous membrane that covers the entire
abdominal cavity. The omentum majus is a large apron-like fold of
visceral peritoneum that hangs down from the stomach.
The mesentery is an organ that attaches the intestines to the posterior
abdominal wall in humans and is formed by the double fold of peritoneum.
Stomach
The stomach has different cells that secrete the following contents:
- The main cells secrete pepsinogen, which is converted to
pepsin within the stomach.
- The wall cells create gastric acid (hydrochloric acid (=zoutzuur))
Pylorus → stomach porter that periodically opens up
Mucosa → mucous membrane which is meant to make the food
flow properly and protect the wall of the stomach from the pepsin.
Contents
- Hormones
- Receptors
- Signal transduction
- Homeostasis
Hormones
Definitie: “Chemical secreted by a (group of) cell(s) into the blood for transport to a distant
target, where it exerts its effect at low concentrations.”
There is some overlap with other signaling molecules that have a likewise function:
IGF (insuline-like growth factor) → Growth factor
CCK (cholecystokinin) → Neurotransmitter
EPO (erythropoietin) → Cytokine
The specialized organs that (solely) produce hormones are:
- Thyroid gland
- Adrenal gland
- Pituitary gland
- Pancreas
Other tissues that produce hormones are:
- Adipose tissue
- Intestines
- Kidneys
- Bones
Hormones regulate:
- Growth and development
- Metabolism
- Reproduction
- Internal environments
They’re also involved in:
- Homeostasis
- Reacting to physical and emotional stress
- Responses to the environment
,Four main receptor types:
1. Receptor channels → binding
opens channel
2. Receptor enzymes → binding
to a receptor enzyme
activates intracellular
enzyme
3. GPCR → binding to GPCR
opens ion channel
4. Integrin receptors → binding
to integrin receptors alters
cytoskeleton
GPCR’s
These are the most common type of receptors in the human body. There are more than 800
different types known. These snake-like structures span the lipid bilayer 7 times before being
coupled to a G protein. GPCR’s are important drug
targets (approx. 40%) and have two different signal
transduction routes:
1. Adenylyl cyclase → vormt ATP om tot drie
cAMP moleculen → Protein kinase A
2. Phospholipase C → heeft of DAG of
IP3 als second messengers:
- DAG → PKC → gefosforyleerd
proteïne → cel respons
- IP3 → calcium opslag open →
cel respons
Intracellular receptors
There are two types of intracellular receptors. Type I resides within the cytoplasm and is
activated there. Once activated, it moves to the nucleus. Type II resides within the nucleus
and waits to be activated.
Homeostasis
Homeostasis consists of different types of setpoints around which the body tries to maintain
its balance. There are fixed setpoints that include:
- calcium, glucose and pH levels
And there are variable setpoints that include:
- Body temperature
, - Ontogenesis (growth)
- Seasonal cycles (e.g. circadian, ovarian)
Digestion
Feedback loops
Positive feedback doesn’t lead to homeostasis, it shuts off
the feedback cycle and leads to critical transitions where
there’s no return. Example: whenever the head of a baby
touches the bottom of the uterus, the muscle cells will release
large amounts of oxytocin.
Metabolism
The body has a mass balance, in which the respiratory system plays a
major role. Every day an average of 9L (2L of food and drink, the rest of
the organs) of fluids enters the intestines. Only 0.1L goes out again.
The peritoneum is the serous membrane that covers the entire
abdominal cavity. The omentum majus is a large apron-like fold of
visceral peritoneum that hangs down from the stomach.
The mesentery is an organ that attaches the intestines to the posterior
abdominal wall in humans and is formed by the double fold of peritoneum.
Stomach
The stomach has different cells that secrete the following contents:
- The main cells secrete pepsinogen, which is converted to
pepsin within the stomach.
- The wall cells create gastric acid (hydrochloric acid (=zoutzuur))
Pylorus → stomach porter that periodically opens up
Mucosa → mucous membrane which is meant to make the food
flow properly and protect the wall of the stomach from the pepsin.
