Hoorcolleges Hormonen & Homeostase
Topic 1: General Principals
Physiology: the knowledge of nature (function of all living organisms)
- the study of the normal functioning of a living organism and its component parts,
including all its chemical and physical processes
- integration of function across many levels of organisation (molecules - cells - tissues -
organs - organ systems etc.)
Homeostasis: continuing motion and changing in response to internal and
external stimuli
- definition 1: the state of equilibrium (balance) between opposing
pressures in the body with respect to various functions and to the
chemical compositions of the fluids and tissues → situation
- definition 2: the ability of the body to maintain a relatively constant
internal environment → activity/ability
- simple model: sphere with all sorts of cell types that remains constant at
the optimal range for the cell type
- but living organisms can not remain constant at the optimal range since there are
changes → a living organism with changes needs to have a buffer zone that dampens
the fluctuations it encounters
● disturbances coming from outside end up in buffer zone where they are
dampened, cells further control the stable situation of inside of cells
● buffer zone is extracellular fluid, because it is between external cells and internal
cells (dampens fluctuations before they can affect internal cells)
- we do not want wild fluctuations, but we do need small fluctuations (such as change of
molecules when eating or drinking, breathing etc.)
Organism in homeostasis:
- external changes: temperature, behaviour of conspecifics (predators, prey or the same
species), diet/fasting, intoxication, trauma/infection
● external changes cause internal change
- internal changes: developmental programs (body of child differs from adult), failure of
cell processes (abnormal cell growth, autoimmune antibodies) → results in loss of
homeostasis
- internal change result in loss of homeostasis which is noticed by receptor system
- if mechanisms compensated with success → wellness (physiology), if compensation fails
→ illness or disease (pathophysiology)
Homeostatic setpoints:
, - fixed setpoints: [Ca] or [Glucose] concentration in blood, body temperature in
warm-blooded animals
- variable setpoints: ontogenesis (growth, various set points over time from child to
adult), temporal cycles (day/night, ovarian cycles, seasonal reproduction, other seasonal
events (migration, hibernation))
- setpoint regulation: if regulated variable is inside desired range → no further action
required, outside range → homeostasis necessary
Regulation of homeostasis: signals from the endocrine system and the nervous system jointly
maintain homeostasis
- they work together to control and regulate homeostasis
Hormones: signals that are produced by a cell system, the cell system senses the change that
is made and procure a signal to bring everything back to normal to create a balance again
- hormones can react to changes but can also regulate the ongoing processes
● respond to changes in the internal balance, physical and emotional stress,
environment (photoperiod, temperature, food availability, predators, conspecifics,
pathogens)
● hormones regulate: internal environment, growth and development, metabolism,
reproduction
Definition hormone: a compound that is produced by a gland not connected to the outside world,
secreted into the blood and has a physiologic or morphogenetic function in the body, usually
distant from the site of production
- endocrine experiment: remove testis led to morphogenetic changes (crest goes away
(kam), less aggressive), when the testis were implanted again the crest comes back and
it gets aggressive again → a compound in the testis has an effect at a different site →
this is how they came up with definition of hormone
- but definition is not entirely correct since hormones can also be synthesized by
organs/tissues having different primary function (brain, pancreas), compounds (Na,
glucose, NO, CO2) can also act as signaling molecules but are not considered
hormones, and the transport medium is not limited to the blood (intercellular fluid)
- so definition: chemical secreted by a cell or group of cells into the blood for transport to a
(distant) target where it acts in very low concentrations (to affect growth, development,
homeostasis, or metabolism)
Endocrinology: the study of what is secreted inside of the body
Endocrine glands:
- pineal gland, hypothalamus (control centre, inside BBB), pituitary gland/hypothesis
(below hypothalamus (outside BBB)), thyroid gland, parathyroids, adrenal glands,
pancreas, ovaries, testes, other tissues that are not endocrine glands (adipose tissue,
stomach, intestine, skin, placenta, kidney)
Classification of hormones:
, - site of production: glandular hormones, tissue hormones, growth factors, pheromones
(receiver is outside of the body (other organism via urine or sweat))
- receptor type: membrane, nuclear
- biochemistry:
● (poly)peptides/(glyco)proteins (peptide or protein
hormones): amino acids in a sequence (glycoproteins are
attached to the polypeptide)
● steroids: 4, 5, or 6 ring structures that differ in side groups,
all derived from cholesterol (cortisol)
● amino acid derivatives: aromatic amino acids, ring
generates signaling capability (epinephrine)
Peptide hormone synthesis:
- preprohormones (large and inactive) are made via normal transcription and translation
- signal sequence directs preprohormone to ER where enzymes cleave signal sequence
off → inactive prohormone is transported to golgi
- in golgi, the prohormone ends up in secretory vesicles that contain enzymes that cleave
prohormone in bio-active peptides
- not lipid soluble, bind to receptor on surface of target cell (secretin)
Steroid hormone synthesis:
- synthesized by different enzymes in gonads or adrenal glands
- lipid soluble so they can pass through cell membrane and bind to steroid hormone
receptors
Amine hormone synthesis:
- amine group remains
- all tyrosine derived: catecholamines (made by modifying side groups of tyrosine) and
thyroid hormones (synthesized from two tyrosines and iodine atoms)
- melatonin is only one which is tryptophan derived
How are they released:
- peptide and amine hormones can be made and
stored in secretory vesicles and are released from
parent cell via exocytosis
- steroid hormones can not be stored in vesicles
(because they can go out of vesicle), they are
synthesized on demand form precursors and
released from parent cell via diffusion
- catecholamines receptor on cell membrane, thyroid
hormones in nucleus
Endocrine signaling:
- endocrine cell recognizes stimulus and secretes hormones into the blood, target cells
with receptors for the hormone respond to the signal
Local communication: if hormones do not need the blood for transport
Topic 1: General Principals
Physiology: the knowledge of nature (function of all living organisms)
- the study of the normal functioning of a living organism and its component parts,
including all its chemical and physical processes
- integration of function across many levels of organisation (molecules - cells - tissues -
organs - organ systems etc.)
Homeostasis: continuing motion and changing in response to internal and
external stimuli
- definition 1: the state of equilibrium (balance) between opposing
pressures in the body with respect to various functions and to the
chemical compositions of the fluids and tissues → situation
- definition 2: the ability of the body to maintain a relatively constant
internal environment → activity/ability
- simple model: sphere with all sorts of cell types that remains constant at
the optimal range for the cell type
- but living organisms can not remain constant at the optimal range since there are
changes → a living organism with changes needs to have a buffer zone that dampens
the fluctuations it encounters
● disturbances coming from outside end up in buffer zone where they are
dampened, cells further control the stable situation of inside of cells
● buffer zone is extracellular fluid, because it is between external cells and internal
cells (dampens fluctuations before they can affect internal cells)
- we do not want wild fluctuations, but we do need small fluctuations (such as change of
molecules when eating or drinking, breathing etc.)
Organism in homeostasis:
- external changes: temperature, behaviour of conspecifics (predators, prey or the same
species), diet/fasting, intoxication, trauma/infection
● external changes cause internal change
- internal changes: developmental programs (body of child differs from adult), failure of
cell processes (abnormal cell growth, autoimmune antibodies) → results in loss of
homeostasis
- internal change result in loss of homeostasis which is noticed by receptor system
- if mechanisms compensated with success → wellness (physiology), if compensation fails
→ illness or disease (pathophysiology)
Homeostatic setpoints:
, - fixed setpoints: [Ca] or [Glucose] concentration in blood, body temperature in
warm-blooded animals
- variable setpoints: ontogenesis (growth, various set points over time from child to
adult), temporal cycles (day/night, ovarian cycles, seasonal reproduction, other seasonal
events (migration, hibernation))
- setpoint regulation: if regulated variable is inside desired range → no further action
required, outside range → homeostasis necessary
Regulation of homeostasis: signals from the endocrine system and the nervous system jointly
maintain homeostasis
- they work together to control and regulate homeostasis
Hormones: signals that are produced by a cell system, the cell system senses the change that
is made and procure a signal to bring everything back to normal to create a balance again
- hormones can react to changes but can also regulate the ongoing processes
● respond to changes in the internal balance, physical and emotional stress,
environment (photoperiod, temperature, food availability, predators, conspecifics,
pathogens)
● hormones regulate: internal environment, growth and development, metabolism,
reproduction
Definition hormone: a compound that is produced by a gland not connected to the outside world,
secreted into the blood and has a physiologic or morphogenetic function in the body, usually
distant from the site of production
- endocrine experiment: remove testis led to morphogenetic changes (crest goes away
(kam), less aggressive), when the testis were implanted again the crest comes back and
it gets aggressive again → a compound in the testis has an effect at a different site →
this is how they came up with definition of hormone
- but definition is not entirely correct since hormones can also be synthesized by
organs/tissues having different primary function (brain, pancreas), compounds (Na,
glucose, NO, CO2) can also act as signaling molecules but are not considered
hormones, and the transport medium is not limited to the blood (intercellular fluid)
- so definition: chemical secreted by a cell or group of cells into the blood for transport to a
(distant) target where it acts in very low concentrations (to affect growth, development,
homeostasis, or metabolism)
Endocrinology: the study of what is secreted inside of the body
Endocrine glands:
- pineal gland, hypothalamus (control centre, inside BBB), pituitary gland/hypothesis
(below hypothalamus (outside BBB)), thyroid gland, parathyroids, adrenal glands,
pancreas, ovaries, testes, other tissues that are not endocrine glands (adipose tissue,
stomach, intestine, skin, placenta, kidney)
Classification of hormones:
, - site of production: glandular hormones, tissue hormones, growth factors, pheromones
(receiver is outside of the body (other organism via urine or sweat))
- receptor type: membrane, nuclear
- biochemistry:
● (poly)peptides/(glyco)proteins (peptide or protein
hormones): amino acids in a sequence (glycoproteins are
attached to the polypeptide)
● steroids: 4, 5, or 6 ring structures that differ in side groups,
all derived from cholesterol (cortisol)
● amino acid derivatives: aromatic amino acids, ring
generates signaling capability (epinephrine)
Peptide hormone synthesis:
- preprohormones (large and inactive) are made via normal transcription and translation
- signal sequence directs preprohormone to ER where enzymes cleave signal sequence
off → inactive prohormone is transported to golgi
- in golgi, the prohormone ends up in secretory vesicles that contain enzymes that cleave
prohormone in bio-active peptides
- not lipid soluble, bind to receptor on surface of target cell (secretin)
Steroid hormone synthesis:
- synthesized by different enzymes in gonads or adrenal glands
- lipid soluble so they can pass through cell membrane and bind to steroid hormone
receptors
Amine hormone synthesis:
- amine group remains
- all tyrosine derived: catecholamines (made by modifying side groups of tyrosine) and
thyroid hormones (synthesized from two tyrosines and iodine atoms)
- melatonin is only one which is tryptophan derived
How are they released:
- peptide and amine hormones can be made and
stored in secretory vesicles and are released from
parent cell via exocytosis
- steroid hormones can not be stored in vesicles
(because they can go out of vesicle), they are
synthesized on demand form precursors and
released from parent cell via diffusion
- catecholamines receptor on cell membrane, thyroid
hormones in nucleus
Endocrine signaling:
- endocrine cell recognizes stimulus and secretes hormones into the blood, target cells
with receptors for the hormone respond to the signal
Local communication: if hormones do not need the blood for transport
