Endocrinology 2 Flashcards
What is the posterior pituitary?
4 steps:
1. what is made and packaged and where
2. what are transported down the cell
3. what are stored and where
4. What is released into blood
- what two hormoens are produced and where do they go
- The posterior pituitary is an extension of the brain that secretes neurohormones made in the hypothalmus
1. Neurohrmone is made and packaged in cell body of neurons
2. vesicles are transported down the cell
3. vesicles containing neurohromone are stored in posterior pituitary
4. neurohormone are released into blood and relases oxytocin in mamary glands and uterus and vasopressin in kidney
- what is the anterior pituitary: how many hormones, what controls release, name of system
- steps (3)
- 6 hormones
- The anterior pituitary is a true endocrine gland that secretes six classic hormones. Neurohormones from the hypothalamus control release of the anterior pituitary hormones. The hypothalamic hormones reach the anterior pituitary through a specialized region of the circulation called a portal system.
- Neurons synthesizing trophic neurohormones release them into capillaries of the portal system => Portal veins carry the trophic neurohormones directly to the anterior pituitary, where they act on the endocrine cells => Endocrine cells release their peptide hormones into the second set of capillaries for distribution
to the rest of the body. - Prolactin (mammary glands), GH (musculoskeletal system), TSH (thyroid gland), ACTH (adrenal cortex), Gonadotropins LH FSH (Ovary and testis)
Growing Bones
1. Peak bone growth for males and females
2. Decreasing bone mass and bone loss age
3. Growing bones in utero, adolescent, adult
4. Diving chondrocytes, chondrocytes, old chdrocytes, osteoblasts
5. bone growth ceases when
- Males around 30, females around 35-40
- Males= decreasing mass with age. Females= bones loss due to menopasue around 50-60
- In Utero: soft bones, cartilage not fully ossified, active growth plates
Adolescent: bones fully ossified, growth plates close towards end of puberty
Adult: growth plates closed and bones loss after 40 years - Dividing chondrocytes add length to bone
chondrocytes produce cartilage
Old chondrocytes disintegrate
Osteoblasts lay down bone on top of cartilage - bone growth ceases when epiphyseal plate fuses
Growth hormone:
what kind of hormone
released from
Stimulated by
inhibited By
Acts in x to stimulate
Receptor
- Peptide hormone
- released from anterior pituitary
- stimulated by GHRH
- inhibited by Somatostatin
- acts in liver to stimulate IGF release
- Receptor a tyrosine kinase
What is IGF-1?
How is it secreted
- Insulin-Like Growth Factor (IGF-1)
- GH acts on the liver to secrete IGF-1
- growth-promoting effects on almost every cell in
the body
- what stimulates bone growth
- Catabolic actions of GH (3)
- Growth depends on
- Growth hormone (GH) stimulates bone growth
- a) Glucose-spring effect: stimulates adipose cells to break dwon stored fat fuelling growth effects
b) Growth effects: increases uptake of amino acids from the blood and enhances cellular proliferation and reduces apoptosis in bone cells, muscle cells and nervous system and immune cells
c) Diabetogenic effect: GH stimulates liver to break down glycogen into glucose fueling growth effects = IGF-1 release - Growth, a complex process, depends on:
Diet and genetics and Hormones and growth factors
Thyroid Hormone Synthesis: 6 steps
- A Na+ -I symporter brings I- into the cell. The pendrin transporter moves I- into the colloid
- Follicular cell synthesizes enzymes and thyroglobulin for colloid
- Thyroid peroxidase adds iodine to tyrosine to make T3 and T4
- Thyroglobulin is taken back into the cell in vesicles.
- Intracellular enzymes separate T3 and T4
from the protein. - Free t3 and T4 enter circulation
TSH:
activates what via what
stimulates
activates
- activates G-protein linked membrane receptors acting via Adenylate cyclase
- Stimulates synthesis and activity of enzymes involved in T4 and T3 synthesis
- activates transcription factors: c-fos, c-myc and stimulates thyroid growth
mechanism of action of thyroid hormones?
- T3 and T4 circulate in blood bound to plasma proteins
- T3 more 3-5X more potent than T4
- T4 converted to T3 in target tissues
- Both bind to nuclear thyroid receptors (form homodimers or heterodimers with retinoic acid receptor)
- Alter gene transcription
What are the 5 functions of thyroid hormones?
Metabolic
Nervous system
growth and development
cardiovascular
muscular
Hyperthyroidism: what is it, causes, symptoms, treatments
Hyperthyroidism: Thyroid hormone excess
Causes:
* tumours
* thyroid-stimulating immunoglobulins (Graves’ disease)
Symptoms: goiter, nervousness, insomnia, anxiety, high heart rate, exophthalmos (Graves’ disease), weight loss.
Treatments: removal of part of
the thyroid gland, drugs blocking
synthesis of T3 and T4 or block
conversion of T4 to T3
Graves’ disease
- Autoimmune disease: Abnormal antibodies against the
TSH receptor are produced - Cause unknown
- Most common cause of hyperthyroidism
- Most common cause of general thyroid enlargement in developed countries
Hypothyroidism:
causes, symptoms, treatments
Hypothyroidism: Thyroid hormone deficiency
Causes:
* under active thyroid gland
* lack of iodine in diet
- Symptoms: goiter, slowed heart rate, slowed speech, fatigue, cold-intolerance, cretinism (infants), stunted growth (infants) and weight gain.
Treatments: exogenous thyroid
hormone T4 (thyroxine)
Iodine deficiency
- Iodine deficiency leaves the thyroid
gland unable to produce T4 and T3 - Lack of negative feedback leads to excess TSH secretion
- TSH stimulates growth of the thyroid gland, goiter may be present
