12.5.1 Define the Terms ‘Hormone’ and ‘Endocrine System’
Hormone:
Chemical messenger secreted by endocrine glands into the bloodstream, regulating distant target organs.
Endocrine System:
Network of glands (e.g., pituitary, thyroid) that secrete hormones to control bodily functions like growth, metabolism, and reproduction.
12.5.2 Describe Location and Function of Major Glands of the Endocrine System
Pituitary (Base of brain):
“Master gland”; regulates other glands (e.g., thyroid, adrenals) via hormones like growth hormone (GH), thyroid-stimulating hormone (TSH).
Parathyroid (Neck, near thyroid):
Secretes parathyroid hormone (PTH) to regulate calcium levels.
Thyroid (Neck):
Secretes thyroxine (T4) and triiodothyronine (T3) for metabolism; calcitonin for calcium homeostasis.
Pancreas (Abdomen):
Secretes insulin (lowers blood sugar) and glucagon (raises blood sugar).
Adrenal (Above kidneys):
Secretes adrenaline (stress response) and cortisol (metabolism, stress).
Testes (Male gonads):
Secrete testosterone for male reproductive development and secondary sexual characteristics.
Ovaries (Female gonads):
Secrete estrogen and progesterone for female reproductive development and pregnancy.
12.5.3 Differentiate Among Problems Associated with Hyper or Hypo Secretion
| Hormone | Hypersecretion | Hyposecretion |
| Somatotrophin (GH) | Gigantism (children), acromegaly (adults). | Dwarfism (children), reduced bone/muscle growth. |
| Thyroid-Stimulating Hormone (TSH) | Hyperthyroidism (overactive thyroid). | Hypothyroidism (underactive thyroid). |
| Vasopressin (ADH) | Water retention, low blood sodium. | Diabetes insipidus (excessive urination, dehydration). |
| Thyroxine (T4) | Hyperthyroidism (weight loss, rapid heart rate). | Hypothyroidism (fatigue, weight gain). |
| Calcitonin | Low blood calcium (rare). | High blood calcium (osteoporosis risk). |
| Adrenaline | High blood pressure, anxiety. | Reduced stress response (rare). |
| Insulin | Hypoglycemia (low blood sugar). | Diabetes mellitus (high blood sugar). |
| Glucagon | Hyperglycemia (high blood sugar). | Hypoglycemia (low blood sugar). |
| Testosterone | Aggression, excessive muscle growth. | Delayed puberty, low libido. |
| Estrogen | Breast tenderness, hormonal imbalances. | Menopause symptoms, osteoporosis. |
| Progesterone | Menstrual irregularities, mood swings. | Infertility, miscarriage risk. |
12.5.4 Describe Negative Feedback with Reference to Insulin and Glucagon
High Blood Sugar:
Pancreas secretes insulin → Cells uptake glucose → Blood sugar decreases → Insulin secretion stops
Low Blood Sugar:
Pancreas secretes glucagon → Liver releases glucose (glycogenolysis) → Blood sugar increases → Glucagon secretion stops
Negative Feedback:
The response (glucose level change) inhibits further hormone release, maintaining blood sugar homeostasis.
12.5.5 Explain How Adrenaline Is Involved in Emergency Conditions
Role:
Adrenaline (epinephrine) is released by adrenal glands during stress (fight-or-flight response).
Effects:
- Increases heart rate and blood flow to muscles.
- Dilates airways for better oxygen supply.
- Mobilizes glucose for energy (via glycogen breakdown).
Example:
In danger (e.g., facing a predator), adrenaline prepares the body for rapid action by enhancing physical performance.