Flashcards in Lecture 35: Thyroid Hormone / Parathyroid Hormone Deck (25):
Prolactin Inhibitory Hormone (PIH) = ?
Prolactin itself is involved in it's own ______ ______.
- Negative Feedback
Where is the thyroid gland?
- Just below the larynx
Thyroid gland structure:
- Small sacs/follicles
- Each follicle is surrounded by follicular cells
Follicular cells make _______ and secrete it into the follicle.
Parafollicular cells make the hormone _____. It can sense how much _____ is in the blood.
- Calcitonin (reduces blood calcium levels)
Iodine reacts with ______. Iodised ___ moves into the follicular cells. Thyroid hormones are released from _____.
- iodised TBG
Effects of thyroid hormone (general):
- Metabolic effects
- Growth (developmental) effects
- Via nuclear receptors that alter the transcription of genes.
- BMR (basal metabolic rate)
What is the Basal Metabolic Rate?
- Body's rate of energy expenditure under basal conditions (person is awake, at phyical and mental rest, lying down, no muscle movement, at a comfortable temperate and fasted 12-18h)
Effects of thyroid hormone (metabolic):
- Increased body heat production (inc oxygen consumption and ATP hydrolysis)
- Stimulate fat mobilisation and oxidation of fatty acids in many tissues. Decreased triglyceride and cholesterol levels.
- Stimulate carbohydrate metabolism, enhance insulin-dependent entry of glucose into cells
- Increase gluconeogenesis and glycogenolysis
- Increased proteolysis. Predominantly from muscle
Effects of thyroid hormone (growth):
- Growth retardation in thyroid deficiency
- Essential for development of fetal and neonatal brain (CNS)
What is Myxoedema?
- Not enough TH (Hyposecretion)
- Low metabolic rate
- Weight gain
- Cold intolerant
- Slow heart rate
What is Graves Disease?
- Hypersecretion of TH
- High metabolic rate
- Weight Loss
- Heat intolerant
- Increased heart rate
- Tissue Swelling
What is Simple Goitre and how is it caused?
- Thyroid gland enlarges with continual stimulation by TSH (loss of negative feedback control as there is an inadequate concentration of iodine to make TH).
1% of calcium is in blood and tissues, in the plasma the reference range is...
- 9.2 - 10.4 mg/mL
Osteoblasts put ______ in the form of hydroaxyapatite back into the bone.
Osteoclasts absorb ______ and put it back into the blood stream.
The importance of Calcitonin:
- Need it to control calcium levels
- In children: osteoclasts liberate 5g of calcium every day
When calcium levels decrease. _______ is secreted.
- Parathyroid hormone
Parathyroid hormones increase....
- Osteoclast activity
- Break down bone to increase calcium levels in blood
- Reduce osteoblast activity
- Less bone deposition (prevention of hydroxyapatite formation)
Calcium regulation: PTH and Calcitonin:
- PTH and Calcitonin have opposite effects on blood calcium concentration
- Both act on bone (have receptors on bone cells) to bone breakdown (PTH) or bone formation (Calcitonin)
- NOT involved with hypothalamus
What happens when blood Ca2+ are low?
Muscle tremors + spasms
Begins as plasma Ca2+ concentration falls to 6mg/dL
At 4mg/dL, larynx tightens, suffocation
What causes hypocalcemia?
- Vitamin D deficiency
- Thyroid tumors
- Underactive parathyroid glands
What effects does hypercalcemia have?
- Nerve and muscle tissue are less excitable