Topic 5 - Hormones & Homeostasis Flashcards
What is the hormone which helps us regulate blood sugar levels?
Insulin
What are the two types of diabetes and what are their causes?
- Type 1 diabetes - caused by an autoimmune disorder
* Type 2 diabetes - caused by obesity
In type 1 diabetes, how much insulin does the body produce?
Little/virtually none
In type 2 diabetes, how much insulin does the body produce?
Normal/above normal
In a healthy person, what are the three main factors which help maintain a normal blood sugar balance?
- Type of food eaten (amount of glucose ingested)
- The pancreas releases insulin which reduces blood glucose levels
- The liver releases stored glucose into the blood as needed to provide energy
Which ethnic groups have higher risks of developing diabetes?
People of South Asian, African-Caribbean and Native American descents
How many people (in 2014) did the WHO estimate to have diabetes?
422 million
In respect to genetics, what is programming hypothesis?
The idea that stresses during pregnancy (eg undernutrition, exposure to toxins/disease) can predispose the offspring in later life to certain conditions (eg high blood pressure/type 2 diabetes)
What happens if there are excessive amounts of glucose in the body?
There can be irreversible damage to proteins in the body which will affect their functions
What is glycation?
Covalent bonding of sugars to proteins
What are advanced glycation end products, or AGEs?
Damaging molecules which are due to persistently high blood sugar levels
Under what circumstances and how are AGEs (advanced glycation end products) produced?
- When there are persistently high blood sugar levels
* Sugars covalently bond to proteins
What parts of the body can AEGs (advanced glycation end products, the result of persistently high blood sugar) damage?
- Blood vessels
- Tissues
- Organs
- Nerves
- Kidneys
- Eyes
- Heart
What type of hormone is insulin?
A polypeptide
What is a polypeptide?
Short chains of amino acids
What are the three stages of insulin production?
- Pre-pro-hormone
- Pro-hormone
- Insulin
What does insulin consist of?
The chain A and chain B components of pre-pro-insulin
What connects the chain A and chain B components of insulin?
- Two disulfide bonds
* Chain A also has a third disulfide bond for additional stabilisation
How many more amino acids does insulin have than pre-pro-insulin?
59
How do beta cells sense the intracellular concentration of ATP?
With their potassium channel
Are the potassium channels open or closed if ATP concentration is high?
Closed
Do beta cells require insulin in order to be able to uptake glucose from blood?
No
How is the level of glucose in beta cells determined?
By the concentration of glucose in the blood
Which two processes convert glucose into ATP?
Glycolysis and the TCA cycle
What kind of channel do beta cells have?
A potassium channel
What happens to the membrane potential of a beta cell when a potassium channel opens?
The cell becomes more negative due to potassium ions (which are positively charged) leaving the cell
Are potassium ions positively or negatively charged?
Positively
What is the term for what happens to the charge of a beta cell when the potassium channel is open and ions have left the cell?
Hyperpolarisation
What are the first steps involved in the synthesis of a polypeptide?
DNA is transcribed to mRNA, then translated into a polypeptide chain
What is a pre-pro-hormone?
An inactive peptide precursor of an inactive pro-hormone
What is a pro-hormone?
An inactive peptide precursor of an active peptide hormone
What causes the calcium channels in beta cell membranes to close?
Hyperpolarisation of the membrane and an intracellular decrease in calcium concentration
Can insulin cross the cell membrane, and why not?
No, because it is a water-soluble polypeptide
What kind of receptors does insulin activate?
Tyrosine kinase receptors
What is a kinase?
A protein which modifies the actions of other proteins
How does a kinase perform its function?
It adds a phosphate group to proteins
What is the term for the action of kinase?
Phosphorylation
What is a dimer?
A molecule/molecular complex consisting of two molecules of the same type linked together
How can glucose enter cells?
By glucose transporter proteins (GLUT)
How are glucose transporter proteins regulated?
By the activation of insulin receptors
Under what conditions can glucose transporter proteins actually transport glucose into the cell?
If insulin receptors are stimulated
Where are glucose transporter proteins located within the cell?
In vesicles within the cytosol
How does insulin affect the storage of glycogen?
Activated insulin receptors stimulate the synthesis of glycogen from glucose and inhibit the breakdown of glycogen into glucose
What does hyperpolarisation mean?
A change to the cell membrane which makes it more negative
What happens if there is an insufficient intake of iodine?
Levels of TSH and TRH will increase
What does excessively high levels of TSH cause, and what is a common symptom of this?
- Hypothyroidism
* A goitre
What condition can extreme iodine deficiency, especially if in early life, cause and what are the symptoms?
- Cretinism
- Poor physical development
- Learning deficiencies
What is glycogenesis?
The process where cells in the muscles/liver convert glucose to glycogen so that it can be stored
What is lipogenesis?
The process which synthesises fats and carbohydrates which can be then stored as adipocytes or in the liver (literally, ‘creating fat’)
What are insulin’s functions?
- To enable cells to take up glucose
- Promote synthesis of molecules to store energy for later
- Promote feelings of satiety
Where are the endocrine cells in the pancreas located?
Islets of Langerhans
Does the pancreas have an endocrine or exocrine role within the body?
Both
Does the pancreas’ endocrine or exocrine system relate to the regulation of blood glucose?
Endocrine
Of all the complications diabetes usually causes, which two cause the majority of issues?
Poor blood supply and nerve damage (which can be due to poor blood supply)
What are some of the areas of the body which suffer complications due to diabetes?
- Neurological system
- Vision
- Hearing
- Cardiovascular system
What is the HP axis?
The hypothalamic-pituitary axis
What does the HP axis do?
It is a signalling mechanism involving the hypothalamus and pituitary glands, which regulate the endocrine glands and certain body tissues
What is thyrotropin-releasing hormone, TRH, and what does it do?
A peptide neurohormone which stimulates the thyroid gland to produce thyroxine
What is thyroid-stimulating hormone, TSH, and what does it do?
It stimulates production of thyroid hormones, which increase metabolic rate and heat
Are T3 and T4 hydrophobic or hydrophilic?
Hydrophilic
Name the tissues/organs which are affected by thyroid hormones?
- All cells
- Liver
- Adipose tissue
- Lungs
- Heart
How do thyroid hormones affect the liver?
- They increase it’s ability to generate glucose
* They also inhibit further production of glycogen from glucose (enhances efficiency of glucose release)
What condition is a common result of iodine deficiency?
An enlarged thyroid, which can cause a goitre to grow
Hypothyroidism (insufficient thyroid hormone production)
What can chronic thyroid deficiency cause?
Cretinism (especially if the deficiency was in early life)
What is cretinism?
An impairment of growth and mental development
What can cause increased production/secretion of thyroid hormones?
TSI - thyroid-stimulating immunoglobulins
How do TSIs effect the body?
- They bind to TSH receptors, mimicking its effects
- This causes excessive amounts of TSH to be secreted into the blood (because TSI levels are not under the control of the HP axis)
What condition can TSIs cause?
Graves’ Disease
What is one of the more common symptoms of Graves’ Disease?
Bulging eyes
What is the name of the condition when blood calcium levels are high?
Hypercalcaemia
What hormone is released in response to high blood calcium levels?
Calcitonin
What do water-soluble peptide hormones bind to?
Surface receptors
What does calcitonin target?
A class of cell called osteoclasts
What is the difference between osteoblasts and osteoclasts?
- Osteoblasts help build bone
* Osteoclasts destroy bone
Why does calcitonin target osteoclasts?
Osteoclasts destroy bone. Calcitonin inhibits their activity, which means that the bone is free to uptake as much calcium from the blood as it wants
Where is the parathyroid gland located?
Behind the thyroid
What is the main regulatory hormone of blood calcium levels?
Parathyroid hormone
How does parathyroid hormone work?
It increases calcium reabsorption, increases calcium release from bone and increases absorption of dietary calcium
What is required in order to raise blood calcium levels?
Parathyroid hormone and the active form of VitD in the blood (calcite ion)
What is the condition which triggers the release of parathyroid hormone and when does it occur?
- Hypocalcaemia
* When blood calcium levels are low
What do lipophilic peptide hormones bind to?
Intracellular receptors
What are the two main ways hormones can be classified?
Hydrophilic or hydrophobic
What do all neurohormones use as their building blocks?
- Amino acids
* Dopamine uses catecholamine but this is derived from the amino acid tyrosine
What do alpha cells secrete?
Glucagon
What do beta cells secrete?
Insulin
If ATP levels are high, what state will the potassium channels be in?
They will be closed
What triggers the ATP-sensitive potassium channels in beta cells to open?
Falling cellular levels of ATP, which is triggered by blood glucose levels dropping
What triggers the voltage-sensitive calcium channels in beta cells to open?
Partial depolarisation of the cell membrane
What triggers insulin to be released into the blood?
An increase in intracellular calcium concentration
What is meant by the term ‘endocrine’?
Relating to or denoting glands which secrete hormones or other products directly into the blood
As well as cortisol, which other hormone is also involved in increasing blood glucose levels and where is it released from?
Glucagon, released from pancreatic alpha cells
What are the names of the two types of thyroid hormones?
What are their abbreviations?
- Thyroxine (T4)
* Triiodothyronine (T3)
What are the names of the two pancreatic hormones?
- Insulin
* Glucagon
How does the digestive tract absorb iodine from the diet?
In the form of iodide
What is iodide trapping?
The storage of iodide which has been transported from a blood capillary to its adjacent follicular cell
Which oxidative enzyme aids iodide ions in forming iodine?
Thyro-peroxidase
Of the two thyroid hormones (thyroxine (T4) and triiodothyronine (T3)), which is the more physiologically active?
Triiodothyronine (T3)
Approximately how much of secreted hormone from the thyroid gland does T4 account for?
70 - 75%
Are the thyroid hormones hydrophilic or hydrophobic?
Hydrophobic
How are the thyroid hormones transported in the blood?
Most are blood bound to carrier proteins
How do thyroid hormones alter cell function?
By interacting with the DNA in the nucleus
How do pancreatic hormones alter cell function?
They activate signalling cascades that involve the activation of protein kinases and the generation of second messenger molecules
Which part of the brain regulates the levels of thyroid hormones circulating in the blood?
- The hypothalamus
* The pituitary gland
What is the HP (hypothalamic-pituitary) axis>
A signalling mechanism which involves the hypothalamus and pituitary gland, which together regulate the other endocrine glands and certain body tissues
Axons in the anterior lobe of the pituitary gland release their neurohormones where?
Into the blood vessels supplying the anterior lobe
Axons extending into the posterior lobe of the pituitary gland secrete their neurohormones where?
Directly into the blood supplying the body
What detects falling blood levels of thyroid hormones?
TRH (thyrotropin-releasing hormone, a peptide neurohormone)
What is the name of the hormone secreted by the anterior pituitary gland into the blood?
TSH (thyroid-stimulating hormone, a peptide neurohormone)
What is the purpose of TSH (thyroid-stimulating hormone)?
To stimulate the production and secretion of T3 and T4, in order to increase metabolic rates and generate heat
What is the purpose of TRH (thyrotropin-releasing hormone)?
It stimulates the production and secretion of TSH and prolactin
How might an increase in the levels of circulating thyroid hormones counteract exposure to cold?
Thyroid hormones increase the body’s metabolism, which includes an increase in the rate of ATP production. This in turn increases the rate at which ATP is consumed and liberates heat to help maintain body temperature
Which process of metabolic reaction consumes most of the ATP generated in a cell?
The sodium/potassium pumps which maintain the ionic gradients between the inside and outside of the cell
What actions can thyroid hormones have on all tissues/organs?
- Increase metabolic rate
- Increase glucose uptake
- Increase the activity of the sodium-potassium pumps
- Increase proteins involved in the TCA cycle
- Increase beta-adrenergic receptors
What actions can thyroid hormones have on liver tissues/organs?
- Increase glycogenolysis
- Increase glucogenisis
- Decrease glycogenisis
What actions can thyroid hormones have on adipose tissue?
- Increase lipolysis
* Decrease lipogenisis
What actions can thyroid hormones have on lung tissue?
- Increase respiration rate
What actions can thyroid hormones have on heart tissue?
- Increase heart rate
* Increase force of contraction
What is the overall effect which thyroid hormones have on the liver?
They increase the liver’s ability to generate glucose to fuel the needs of the body, either from the breakdown of glycogen into glucose, or the production of glucose from non-carbohydrate molecules such as amino acids, lactate and fatty acids
How might a lack of iodine affect homeostatic function of the thyroid gland?
It will have an effect on the production of T3 and T4. This reduction will in turn cause the hypothalamus and anterior pituitary gland to produce excessive levels of TRH and TSH in an attempt to stimulate the thyroid gland to produce/secrete more thyroid hormones
What bodily effect can high levels of circulating TSH cause?
The thyroid gland to grow, often forming a goitre
How can the binding of TSH (thyroid-stimulating) hormone to its receptors on the cells of the thyroid gland be disrupted?
By thyroid-stimulating immunoglobulins (TSIs)
What are TSIs (thyroid-stimulating antibodies)?
How do they affect thyroid hormones?
- Antibodies produced by the immune system which also stimulate the thyroid gland
- They bind to TSH receptors, which mimicks the effects of TSH
What is the name of the condition caused by TSIs?
Graves disease
What micronutrient is the thyroid gland also involved in the regulation of?
Calcium
What is hypercalcaemia?
High blood calcium levels
What is the peptide hormone related to calcium which the thyroid gland can relase?
Calcitonin
What is calcitonin?
A hormone secreted in the thyroid gland in response to high levels of blood calcium
What are osteoblasts?
Cells which incorporate calcium into new bone
What are osteoclasts?
Cells which destroy bone
What is parathyroid hormone?
A hormone secreted by the parathyroid gland in response to low blood calcium
What is parathyroid hormone’s effect on the body?
It acts on the kidney tubules to increase calcium reabsorption and also increases calcium release from bone and the activation of vitamin D to increase absorption of dietary calcium
Which hormone is released, and from which gland, to reduce calcium levels
- Calcitonin
* The thyroid gland
What is required in the blood to raise calcium levels?
- Parathyroid hormone
* The active form of vitamin D
What body functions does the pineal gland regulate?
- Regulation of sleep
* The body clock
What body functions does the hypothalamus regulate?
The endocrine system which regulates other endocrine tissues within the body
What body functions does the pituitary gland regulate?
- Metabolic rate
- Growth and development
- Fertility and reproduction
- Stress
What body functions does the thyroid gland regulate?
- Metabolic rate
* Calcium homeostasis
What body functions does the parathyroid gland regulate?
Calcium homeostasis
What body functions does the stomach regulate?
- Gastric acid production
* Feelings of hunger
What body functions does the liver regulate?
- Growth
- Blood pressure
- Production of platelets
What body functions do the adrenal glands regulate?
Acute/chronic stress responses
What body functions does the pancreas regulate?
Blood glucose levels
What body functions do the kidneys regulate?
- Erythrocyte production
* Calcium homeostasis
What body functions does the duodenum regulate?
Digestive processes
What body functions does adipose tissue regulate?
Satiety
What body functions do the ovaries regulate?
- Sexual development
- Fertility
- Reproduction
What body functions do the testes regulate?
- Sexual development
* Fertility
What are the two broad groups which hormones can be classified into?
- Water-soluble (hydrophilic)
* Fat-soluble (hydrophoblic/lipophilic)
Can water-soluble hormones easily diffuse across cell membranes?
No
Can lipid-soluble hormones easily diffuse across cell membranes?
Yes
Which are the catecholamine hormones that are synthesised from the amino acid tyrosine?
- Adrenalin
- Noradrenalin
- Dopamine
Aside from catecholamines, what other class of hormones are synthesised from tyrosine?
Thyroid hormones
What is the parent molecule which all steroid hormones in humans are derived from?
Cholesterol
How does cholesterol influence the properties of the plasma membrane?
It maintains the fluidity of the plasma membrane
How many rings of fused carbon do all the steroid hormones have?
Four
Which are the three main glands where steroid hormones are synthesised?
- The adrenal gland (cortex)
- Testes
- Ovaries
What are eicosanoids?
Hormones synthesised from fatty acids found in the plasma membrane
How do eicosanoids exert their action?
They activate membrane receptors coupled to G-proteins
Are eicosanoids classed as water or lipid-soluble hormones?
Water-soluble
What effects can eicosanoids mediate?
- Pain
- Inflammation
- Fever
- Immune response
- Cell growth
- Blood pressure
Which common drug works by preventing the production of eicosanoid hormones?
Aspirin
Which gas can act as a hormone?
Nitric oxide
What role does nitric oxide play within tissues?
It is critical to the process of regulating blood flow within tissues
In which part of the tissue is nitric oxide produced?
The endothelial cells that line the blood vessels
Which amino acid is used in the production of nitric oxide?
Arginine
What effect does nitric oxide have on tissues?
It causes nearby vascular smooth muscle to relax, increasing blood flow in the surrounding tissue
Which group of people produce more nitric oxide, particularly in the lungs?
Those who live at high altitudes
Particularly with regards to homeostasis, what is positive feedback?
A cyclic feedback loop which acts on itself to increase the activity that initiated the feedback, producing ever-increasing levels of activity
Which biological process is an example of a positive feedback system?
Childbirth; high levels of oxytocin in the blood cause the uterus to contract with ever-increasing frequency. This process of positive reinforcement continues until the baby is born, when the stimuli to signal further release of oxytocin stop