The Endocrine System Flashcards
(114 cards)
1
Q
Direct communication
A
Occurs between two cells of the same type in extensive physical contact
2
Q
Gap junctions
A
- Coordinate ciliary movement among epithelial cells
- Coordinate the contractions of cardiac muscle cells
- Facilitate the propagation of action potentials from one neuron to the next at electrical synapses
3
Q
Paracrine communication
A
Messages occur between cells within a single tissue
4
Q
Autocrine communication
A
Occurs when the messages affect the same cells that secrete them
5
Q
Endocrine communication
A
Occurs when the endocrine system uses hormones to relay information and instructions between cells in distant portions of the body
6
Q
Target cells
A
Specific cells in other tissues that have the receptors needed to bind and read hormonal messages
7
Q
Synaptic communication
A
Neurons release neurotransmitter at a synapse very close to target cells that have the appropriate receptors
8
Q
Differences between endocrine and nervous communication
A
Nervous: split-second, specific, short-lived
Endocrine: slow, affect all cells, long-lasting
9
Q
Similarities of nervous and endocrine communication
A
- Rely on the release of chemicals that bind to specific receptors on their target cells
- Share chemical messengers
- Regulated mainly by negative feedback control mechanisms
- Aim to control homeostasis
10
Q
Major processes affected by hormones
A
- Growth and development
- Reproduction
- Regulation of cell metabolism and energy balance
- Regulation of body water content and levels electrolytes and organic nutrients
- Mobilisation of body defences
11
Q
Endocrine cells
A
Glandular secretory cells that release their secretions into the extracellular fluid
12
Q
Exocrine cells
A
Secrete their products onto epithelial surfaces through ducts
13
Q
Classes of hormones
A
- Amino acid derivatives
- Peptide hormones
- Lipid derivatives
14
Q
Amino acid deriatives
A
- Synthesised from amino acids tyrosine (thyroid hormones, E, NE and dopamine) and tryptophan (melatonin)
15
Q
Peptide hormones
A
Glycoproteins and short polypeptides and small proteins
16
Q
Lipid derivatives
A
- Eicosanoids
2. Steroid hormones
17
Q
Eicosanoids
A
Signalling molecules including leukotrienes, prostaglandins, thromboxanes and prostacyclins
18
Q
Inactivation of hormones
A
A freely circulating hormone remains functional for less than 1 hour
It is inactivated when:
- It diffuses out of the bloodstream and binds to receptors on target cells
- It is absorbed and broken down by cells of the liver or kidneys
- It is broken down by enzymes in the blood or interstitial fluids
19
Q
Binding of a hormone
A
- Alter genetic activity
- Alter the rate of protein synthesis
- Change membrane permeability
20
Q
Hormone receptor
A
Protein molecule to which a particular molecule binds strongly
21
Q
Why do hormones have different effects on different tissues?
A
Cells have different combinations in different tissues
22
Q
Down regulation
A
A process in which the presence of a hormone triggers a decrease in the number of hormone receptors
Cells become less sensitive to high levels of a particular hormone
23
Q
Up regulation
A
A process in which the absence of a hormone triggers an increase in the number of hormone receptors
Cells become more sensitive to low levels of a particular hormone
24
Q
Extracellular receptors
A
E, NE and dopamine
Peptide hormones
(Can’t penetrate a plasma membrane because they aren’t lipid soluble)
25
First messenger
A hormone that binds to an extracellular receptor
26
Second messenger
An intermediary molecule that appears due to a hormone-receptor interaction
27
Amplification
When a small number of hormone molecules binds to extracellular receptors, thousands of second messengers may appear in a cell
28
G protein
An enzyme complex coupled to a membrane receptor that serves as a link between the first and second messenger
29
Increasing cAMP level
1. Activated G protein activates the enzyme adenylate cyclase
2. Adenylate cyclase converts ATP to cAMP
3. cAMP functions as a second messenger by activating kinase
4. Generally cAMP activates kinase that phosphorylate proteins which have an effect on the cell
30
Phosphodiesterase (PDE)
Inactivate cAMP by converting it to AMP
31
Effects of cAMP
Metabolic activity of the cell accelerated
32
Opening of calcium ion channels
1. G protein first activates the enzyme phospholipase C (PLC)
2. This enzyme triggers a receptor cascade that begins with the production of DAG and IP3 from membrane phospholipids
3. IP3 diffuses into the cytoplasm and triggers the release of CA2+ from intracellular reserves
4. Combination of DAG and intracellular calcium ions activates protein kinase C (PKC) > phosphorylation of calcium ion channel proteins
5. Calmodulin binds with calcium ions which can activate specific cytoplasmic enzymes
33
Which hormones target intracellular receptors?
Mostly steroid and thyroid hormones
34
Steroid hormones
Alter the rate of DNA transcription in the nucleus and so change the pattern of protein synthesis
35
Thyroid hormones
Activate specific genes or change the rate of transcription
36
Negative feedback
A stimulus triggers the production of a hormone whose direct or indirect effects reduce the intensity of the stimulus
37
Triggers of hormone secretion
1. Humoral stimuli: changes inextracellular fluid
2. Hormonal stimuli: arrival of specific hormone
3. Neural timuli: arrival of neurotransmitters
38
Infundibulum
Connects the hypothalamus to the pituitary gland
39
3 mechanisms of hypothalamic control over endocrine function
1. Production of ADH and OXT > release of ADH and OXT from posterior lobe
2. Secretion of regulatory hormones to control activity of the anterior lobe of the pituitary gland > hormones secreted by the anterior lobe control other endocrine organs
3. Control of sympathetic output to adrenal medulla > secretion of E and NE from adrenal medulla
40
Adenohypophysis
Anterior lobe of the pituitary gland
41
3 regions of adenohypophysis
1. Pars distalis: largest
2. Pars tuberalis: extension
3. Pars intermedia: narrow band
42
Fenestrated capillaries
Allow relatively large molecules to enter or leave the bloodstream
43
Blood supply to pituitary gland
1. Superior hypophyseal artery delivers blood to a capillary network in the upper infundibulum
2. Inferior hypophyseal artery delivers blood to the posterior lobe of the pituitary gland
44
Blood leaving pituitary gland
1. Portal vessels deliver blood containing regulatory hormones to the capillary network in the anterior lobe of the pituitary
2. Hypophyseal veins carry blood containing the pituitary hormones to the cardiovascular system for delivery to the rest of the body
45
Portal vessels
Link two capillary networks
46
Benefits of hypophyseal portal system
Ensures that all the hypothalamic hormones entering portal vessels reach the target cells in the anterior lobe before being diluted through mixing with general circulation
47
Releasing hormone (RH)
Stimulates the synthesis and secretion of one or more hormones at the anterior lobe
48
Inhibiting hormone (IH)
Prevents the synthesis and secretion of hormones from the anterior lobe
49
Thyroid stimulating hormone (TSH)
Targets the thyroid gland and triggers the release of thyroid hormones
50
Adrenocorticotrophic hormone (ACTH)
Stimulates the release of steroid hormones by the adrenal cortex
Affect glucocorticoids (glucose metabolism)
51
Gonadotropins
Regulate activities of the gonads
1. Follicle-stimulating hormone
2. Luteinizing hormone
52
Follicle-stimulating hormone
Promotes follicle development in females
| Stimulates the secretion of estrogens
53
Luteinizing hormone
Females
Induces ovulation
Promotes ovarian secretion of estrogens and progestrone
Males
Stimulates production of androgens
54
Hypogonadism
Caused by abnormally low production of gonadotropins
| Prevents sexual maturation in children
55
Prolactin (PLR)
Stimulates mammary gland development in females
56
Growth hormone (GH)
Stimulates cell growth and division by accelerating rate of protein synthesis
57
Neurohypophysis
Posterior lobe of pituitary gland
| Contains the axons of hypothalamic neurons
58
Supra-optic nuclei
Produce ADH
59
Paraventricular nuclei
Produce OXT
60
ADH
Released in response to an increase in the solute concentration in the blood or a decrease in blood volume or pressure
Acts on the kidneys to retain water and decrease urination
61
OXT
Women
Stimulates smooth muscle contraction in the wall of the uterus, promoting L&D
Stimulates ejection of milk
Men
Stimulates smooth muscle contraction in the sperm duct and prostate gland
62
Thyroid gland
Ductless gland in the neck that secretes hormones regulating growth, development and metabolism
63
Isthmus
Connect two lobes of thyroid gland
64
C cells
Lie between cuboidal follicle cells and their basement membrane
65
Follicle cavity
Holds colloid fluid
| Surrounded by follicle cells
66
Thyroid hormones
T3 and T4
Regulated by thyroid-stimulating hormone
67
Synthesis of thyroid hormones
1. Iodide ions are absorbed from the digestive tract delivered to the thyroid gland by the bloodstream
2. Iodide ions diffuse to the apical surface of each follicle cell where they are converted into an atom of iodine. The tyrosine portion of thyroglobulin bind the iodine atoms
3. Iodine-containing thyroxine molecules become linked to form T3 and T4
4. Follicle cells remove thyroglobulin from the follicles by endocytosis
5. Lysosomal enzymes break down the thyroglobulin and the amino acids and thyroid hormones enter the cytoplasm
6. The released T3 and T4 diffuse from the follicle cell into the bloodstream
7. A majority of the T3 and T4 bind to transport proteins
68
Functions of thyroid hormones
Depend on location of hormones:
1. Cytoplasmic receptors: storage
2. Mitochondria: increase rates of ATP production
3. In the nucleus: activates genes that control synthesis of enzymes involved in energy activation and use
69
Calorigenic effect
Thyroid hormones also activate genes that code for enzymes involved in glycolysis and ATP production, increasing metabolic rate of the cell
70
Calcitonin
Produced by C cells of the thyroid gland
| Helps to regulate Ca2+ concentration in body fluids
71
Parathyroid glands
Four
Parathyroid cells produce parathyroid hormone
Parathyroid oxyphil cells
72
Parathyroid cells
Monitor the circulating concentration of calcium ions
| Secrete PTH when Ca2+ blood concentration falls
73
Effects of parathyroid hormones
1. Mobilises calcium from bone by affecting osteoblast and osteoclast activity
2. Enhances the reabsorption of Ca2+ by the kidneys, reducing urinary loss
3. Stimulates the formation and secretion of calcitriol by the kidneys
74
Adrenal glands
Two
| Adrenal cortex produces steroid hormones
75
Corticosteroids
Steroid hormones produced by adrenal glands
| Exert their effects by turning on transcription of certain genes in the nuclei of the target cells
76
Zones of the adrenal cortex
1. Outer zona glomerulosa
2. Middle zona fasciculata
3. Inner zona reticularis
77
Zona glomerulosa
Outer
| Produces mineralocorticoids
78
Mineralocorticoids
Steroid hormones that affect the electrolyte composition of body fluids
79
Aldosterone
Main mineralocorticoid of the zona glomerulosa
| Stimulates conversation of sodium ions and elimination of potassium ions
80
Zona fasciculata
Middle
| Produces glucocorticoids
81
Glucocorticoids
When stimulated by ACTH, zona fasciculata secretes cortisol, corticosterone and cortisone
Speed up the rate of glucose synthesis and glycogen formation
Also anti-inflammatory
82
Zona reticularis
When stimulated by ACTH, zona reticularis secretes small amounts of androgens
83
Adrenal medulla
Secretes E and NE
84
Pineal gland
Main part of the epithalamus
| Contains neurons, neuroglia and pinealocytes
85
Pinealocytes
Synthesise melatonin from seratonin
86
Functions of melatonin
1. Influencing circadian rhythyms
2. Inhibiting reproductive functions
3. Protecting against damage by free radicals
87
Exocrine pancreas
Consists of clusters of gland cells and their attached ducts
Secrete an alkaline, enzyme-rich fluid that reaches the lumen of the digestive tract through a network of secretory ducts
88
Endocrine pancreas
Small groups of cells scattered among the exocrine cells
89
Pancreatic islets
Clusters in endocrine pancreas
90
Pancreatic islet cells
Alpha, beta, delta and pancreatic polypeptide cells
91
Alpha cells
Produce glucagon which raises blood glucose level
92
Beta cells
Produce insulin which lowers blood glucose level
93
Delta cells
Produce peptide hormone which supresses the release of glucagon and insulin
94
Pancreatic polypeptide cells
Produce pancreatic polypeptide which inhibits gallblader contractions and regulates the production of some pancreatic enzymes
95
Effects of insulin
1. Accelerating glucose uptake
2. Accelerating glucose use
3. Stimulating glycogen formation
4. Stimulating amino acid absorption and protein synthesis
5. Stimulating triglyceride formation
Decreases blood glucose levels
96
Effects of glucagon
1. Stimulating the breakdown of glycogen
2. Stimulating the breakdown of triglycerides
3. Stimulating the production and release of glucose
Increases blood glucose levels
97
Diabetes mellitus
Glucose accumulates in the blood and urine as a result of faulty glucose metabolism
98
Calcitriol
Steroid hormone secreted by the kidneys in response to PTH
| Stimulates calcium and phosphate ion absorption along the digestive tract
99
Eryhtropoietin
Peptide hormone secreted by the kidneys in response to low oxygen levels in kidney tissues
Stimulates red bone marrow to produce RBCs
100
Renin
Released by specialised kidney cells in response to
1. Sympathetic stimulation
2. A decline in renal blood flow
Functions as an enzyme that starts RAAS cascade (BP regulation and electrolyte metabolism)
101
RAAS
1. Renin converts to angiotensinogen
2. ACE modifies angiontensin I to angiotension II
3. Angiotension II secretes aldosterone
102
Natriuretic peptides
If blood volume becomes too great, endocrine cells are stretched excessively to the point which they begin to secretes natriuretic peptides
Promote the loss of Na+ and water by the kidneys
103
Thymus
Located in the mediastinum
104
Interstitial endocrine cells
In males, produce androgens
105
Nurse cells
Support differentiation and physical maturation of sperm
| Secrete inhibin under FSH stimulation
106
Estrogen
Produced in females in the ovaries under FSH and LH stimulation
107
Leptid
Peptide hormone produced by adipose tissue
Feedback control of appetite
108
Hormonal effects
1. Antagonistic: opposing
2. Synergistic: additive
3. Permissive: one is needed for the other
4. Integrative: different but complementary results
109
Hyperglycemia
High glucose levels in the blood
110
Glycosuria
Glucose appears in the urine
111
Polyuria
Urine volume becomes excessive
112
Type 1 diabetes
Inadequate insulin production by the pancreatic beta cells
113
Type 2 diabetes
Normal insulin production but tissues don't respond properly
114
3 phases of general adaptation syndrome
1. Alarm phase (flight or fight, sympathetic division of the ANS)
2. Resistance phase (glucocorticoids)
3. Exhaustion phase (eventual breakdown of homeostatic regulation and failure of one or more organs
