Hormones, tissues and basics Flashcards
(26 cards)
What is homeostasis?
Organisms maintain relatively stable internal environment - concentration of substances are kept in certain ranges.
When internal or external changes happen, to maintain homeostasis, organisms tries to compensate concentration of substances back to the normal ranges.
If compensation fails, it leads to the disease.
What are the 4 main types of tissues and their key features?
1) Epithelial - basal lamina (collagen, laminin, proteoglycans) as matrix, no direct blood supply, has microvilli or cilia, found at surfaces, cells in layers, regularly shaped cells (flattened, cuboidal, columnar); tight and gap junctions.
2) Connective - diverse matrix types, cartilage does not have blood supply, supports organs, forms blood, bone and cartilage, cells reside randomly, irregular or round cells.
3) Muscle - external lamina as matrix, generates force, movement and electrical signals, elongated (skeletal and heart muscle) or spindle (smooth muscle) shaped cells in sheets, bundles, branched in heart muscle.
4) Nervous - external lamina as matrix, generates and conducts electrical signals, highly elongated and branched cells form networks or exist on their own
What is extracellular matrix?
The substances (usually fibres) produced by cells which connect and support cells in the tissue outside their membranes.
Key molecules in the extracellular matrix - proteoglycans with a core protein on its axis, and multiple polysaccharide chains branching away from it like feather.
What are the 3 main types of cell junctions?
1) anchoring, either cell-to-cell or to the extracellular matrix.
2) tight (occluding) junctions to prevent substances from passing between cells in the tissue.
3) Gap junctions: tiny intercellular channels (cytoplasmic bridges) for rapid direct communication between adjacent cells.
What are the 7 types of connective tissues?
1) loose: gel matrix (ground substance>fibres/cells), randomly arranged fibres (different sorts, including collagen and elastin) produced by fibroblasts under epithelia/endothelium.
2) dense irregular: randomly arranged collagen fibres (little ground substance) produced by fibroblasts at muscle and nerve sheath.
3) dense regular: parallelly arranged collaged fibres (little ground substance) produced by fibroblasts at tendons and ligaments.
4) adipose tissue: no fibres and very little ground substance, brown (to maintain body temperature) and white (to store energy) fat cells; found under skin, around liver and other abdominal organs (visceral fat) and in bone (yellow bone marrow).
5) blood: aqueous matrix, erythrocytes, leukocytes and platelets in blood and lymph vessels.
6) cartilage: contains hyaluronic acid and collagen in firm but flexible matrix, produced by chondroblasts; protects and supports joint surfaces, makes ears, nose and larynx rings.
7) bone: contains calcium salts (and few collagen) in very rigid matrix; osteoblasts and osteocytes.
What are the 4 types of epithelia?
1) exchange: squamous cells in endothelium (the innermost layer of blood vessels) with pores allowing leakage of nutrients into extracellular fluid and taking up waste away from extracellular fluid; or in alveoli with tight junctions for gas exchange.
2) transport: columnar cells; selectively permeable, substances (from lumen of intestine or kidney) must pass through folded apical and than flat basolateral membrane to enter extracellular fluid; tight junctions to prevent leakage.
3) ciliated: columnar cells; beating cilia to sweep away pathogens, dirt and mucous in respiratory tract (except bronchioles with simple columnar and cuboid).
4) secretory: Goblet cells secrete mucous (both in respiratory and gastrointestinal tract); glands produce endocrine (hormones) and exocrine (digestive enzymes) secretions.
What is a hormone?
A signalling chemical released in the blood to act on the targets (receptors on cell surface or in cytoplasm) at the great distances, and which gives biological effects (changing rates of enzyme reactions, regulating transport and gene expression) at extremely low (nanomolar or picomolar) concentrations.
What are the 3 types of hormone interactions?
- synergistic: combined effect > sum of the individual effects (glucagon + cortisol + adrenaline for blood glucose).
- permissive: one hormone can fully perform its effect only in the presence of other hormones (thyroid hormone + gonadotropins for sexual maturation).
- antagonistic: opposing effects (insulin lowers blood glucose, glucagon increases blood glucose).
What are the main types of hormones?
- peptide
- steroid
- amine (catecholamines)
- amine (thyroid)
What are the features of peptide hormones?
- made and stored in advance in secretory vesicles
- released through exocytosis
- dissolved in plasma during blood transport (water soluble)
- short half-life (unstable, act for short time)
- target cell membrane
- activate second messenger systems (sometimes gene expression)
- result in both protein modification and synthesis of new ones
- insulin, glucagon, parathyroid hormone, vasopressin, angiotensin
What are the features of steroid hormones?
- made on demand from precursors
- released through simple diffusion (steroids are non-polar)
- transported in blood on carrier protein due to being insoluble in water
- long half-life (stable, act for long time)
- target nucleus or cytoplasm, sometimes cell surface
- mostly activate gene expression, resulting in the synthesis of new proteins
- oestradiol, testosterone, cortisol, aldosterone
What are the features of amine hormones called catecholamines?
- made in advance and stored in secretory vesicles
- leave though exocytosis
- transported dissolved in blood plasma (water soluble)
- short half-life (unstable, act for short time)
- target cell membrane
- activate second messenger systems
- modification of existing proteins
- adrenaline, noradrenaline, dopamine (tyrosine derived)
What are the features of amine hormones called thyroid hormones?
- precursors are stored in secretory vesicles
- released through transport proteins in cell membrane
- transported in blood on protein carriers (water insoluble)
- long half-life (stable, act for long time)
- target nucleus
- activate gene expression to make new proteins
- thyroxine and triiodothyronine
How peptide hormones are produced?
Analogically to protein trafficking in general:
1) preprohormone: huge peptide with ER signal sequence, connected copies (6 copies in thyrosin-releasing hormone) or related hormones (3 different in pro-opiomelanocortin) and extra sequences.
2) prohormone: in ER lumen, signal sequence is removed with signal peptidase.
3) prohormone (still inactive) travels through Golgi complex
4) active hormone: in secretory vesicle, other peptidases cut off extra pieces (C-peptide in insulin) and separate copies before exocytosis.
What is the parent compound for all steroid hormones?
Cholesterol - amphipathic compound with 4 rings.
How do steroid hormones act exactly?
1) dissociate from from protein carriers
2) enter cytoplasm through simple diffusion and bind to cytoplasmic or karyoplasm receptor
3) hormone-receptor complex enters nucleus through nuclear pore (if bound in cytoplasm) and bind to DNA
4) the target gene is expressed and mRNA moves to cytoplasm
5) new proteins are synthesised
Alternatively: bind to the surface cell receptors and trigger rapid responses with second messenger system.
What is the chemical difference between catecholamines and thyroid hormones?
Catecholamines (G-protein coupled):
- only one tyrosine molecule is used
- carboxyl group is removed
- aromatic ring is not modified
- adrenaline and noradrenaline have an extra hydroxyl group in the linear part
- adrenaline is methylated next to amino group
Thyroid hormones (nuclear receptors):
- made of 2 molecules of tyrosine (2 aromatic rings connected with an ether bond)
- iodine is attached to aromatic rings (2+2 for thyroxine, 1+2 for triodothyronine)
- carboxylic group is not removed, amino group is not modified.
What are the reflexes which control hormone release?
Feedback loops, often with nervous system involvement.
Simple reflexes: one or multiple stimuli result in release of a single hormone (parathyroid hormone and insulin correspondingly).
Complex reflexes: many hormones acting in hierarchy with multiple integrating centres (hypothalamic-pituritary hormones).
How does parathyroid hormone act?
Simple one-stimulus reflex:
low plasma Ca2+ is sensed by parathyroid cell and it releases parathyroid hormone to reach bone and kidney to increase Ca2+ reabsorption.
Additionally, calcitriol is increased and more Ca2+ is absorbed by large intestine.
Ca2+ in plasma increases - response inhibits the beginning of cycle.
How does insulin act?
Simple multiple-stimuli reflex:
1a) eating meal stimulates sensory neuron in digestive tract, CNS is an integrating centre, efferent neuron stimulates pancreas.
1b) increased concentration of glucose in digestive tract stimulates cells in small intestine to produce GLP-1, which stimulates pancreas.
1c) high blood glucose directly stimulates beta-cells in pancreas by increasing ATP production there.
2) pancreas releases insulin to target tissues (mainly adipose and muscle) to increase glucose uptake
3) blood glucose lowers - response provides negative feedback.
What is the structure of pituitary gland?
Anterior (to face) pituitary (adenohypophysis): epithelial origin, true endocrine tissue.
After being triggered by hypothalamic neurohormones from portal system, secretes prolactin, growth hormone, thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), luteinizing hormone and follicle stimulating hormone.
Posterior (to back) pituitary (neurohypophysis): extension of neural tissue. Connected to brain with infundibulum, just below hypothalamus.
Stores and secretes oxytocin and vasopressin into vein (but they are produced in hypothalamus and transported down to posterior pituitary through vesicles in neuron cell body)
Whole pituitary is found in sphenoid bone pocket.
What are trophic hormones?
Hormones which target other endocrine glands to trigger release of other hormones.
What is the order of some hormone regulation pathways?
- Dopamine inhibits prolactin –> lactation
- Thyrotropin-releasing hormone (TRH) –> thyroid stimulating hormone (TSH) –> thyroid hormones
- Corticotropin-releasing hormone (CRH) –> adrenocorticotropic hormone –> cortisol
- Growth-hormone-releasing hormone (GHRH) –> growth hormone –> insulin-like growth factors (secreted by liver)
Somatostatin inhibits growth hormone. - Gonadotropin-releasing hormone –> FSH and LH (gonadotropins) –> androgens and oestrogens –> germ cell development into gametes.
What are the features of the complex reflex using hypothalamic-anterior pituitary pathway?
There are multiple negative feedbacks, often in the middle of the pathway.
For example, growth hormone (second) from anterior pituitary inhibits growth-hormone-releasing hormone (first) from hypothalamus; insulin-like growth factors (third) from the liver inhibit both growth hormone (second) and growth-hormone-releasing hormone (first).
