Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Identify the major endocrine glands and their hormones.
• Explain the mechanism of hormone action.
• Discuss the regulation of blood glucose levels.
• Describe negative feedback mechanisms in hormone regulation.
• Explain the hormonal control of the menstrual cycle.

Lesson summary

The endocrine system plays a vital role in maintaining homeostasis, the stable internal environment essential for our survival. In South Africa, understanding this system is particularly important due to the prevalence of conditions like diabetes and thyroid disorders, which affect many communities. This week, we will delve into the human endocrine system, focusing on the glands, hormones they produce, and how these hormones regulate various bodily functions to maintain homeostasis. Understanding these processes is crucial not only for your Life Sciences grade but also for making informed decisions about your health and the health of your community.

Lesson notes

The endocrine system is a network of glands that secrete hormones directly into the bloodstream. These hormones travel throughout the body, affecting specific target cells that possess receptors for that particular hormone. This allows for communication and coordination of various physiological processes to maintain homeostasis. 2.

1. Major Endocrine Glands and Hormones: Pituitary Gland: Often called the "master gland" because it controls other endocrine glands. Located at the base of the brain.

It has two lobes: Anterior Pituitary:* Produces and secretes hormones such as: Growth Hormone (GH): Stimulates growth and development, particularly in bones and muscles. Malfunctions can lead to gigantism (excess GH during childhood) or dwarfism (insufficient GH during childhood). In adults, excess GH causes acromegaly (enlargement of hands, feet, and face).

Thyroid-Stimulating Hormone (TSH): Stimulates the thyroid gland to produce thyroid hormones.

Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal cortex to produce cortisol. Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH): These are gonadotropins that regulate the function of the ovaries and testes. In females, they regulate the menstrual cycle and ovulation. In males, they stimulate sperm production and testosterone secretion.

Prolactin: Stimulates milk production in mammary glands.

Posterior Pituitary:* Stores and releases hormones produced by the hypothalamus: Antidiuretic Hormone (ADH) (Vasopressin): Increases water reabsorption in the kidneys, reducing urine volume. A deficiency leads to diabetes insipidus, characterized by excessive thirst and urination. Imagine a learner in Durban not being able to concentrate in class due to constant thirst and needing to use the restroom frequently.

Oxytocin: Stimulates uterine contractions during childbirth and milk ejection during breastfeeding.

Thyroid Gland: Located in the neck.

Produces: Thyroxine (T4) and Triiodothyronine (T3): Regulate metabolism, growth, and development. Iodine is essential for their production. Iodine deficiency is a significant public health concern, especially in inland areas. This is why iodized salt is important. Hypothyroidism (underactive thyroid) causes weight gain, fatigue, and slowed heart rate. Hyperthyroidism (overactive thyroid) causes weight loss, anxiety, and rapid heart rate. Goitre, an enlargement of the thyroid gland, can result from iodine deficiency.

Calcitonin: Lowers blood calcium levels by promoting calcium deposition in bones.

Parathyroid Glands: Located on the posterior surface of the thyroid gland.

Produces: Parathyroid Hormone (PTH): Increases blood calcium levels by stimulating calcium release from bones and increasing calcium absorption in the intestines and kidneys.

Adrenal Glands: Located on top of the kidneys.

Consists of two parts: Adrenal Cortex:* Produces: Cortisol (Glucocorticoid): Regulates metabolism, immune function, and stress response.

Aldosterone (Mineralocorticoid): Regulates sodium and potassium balance in the kidneys, affecting blood pressure. Imagine someone with low blood pressure struggling to stand after sitting, possibly linked to aldosterone issues.

Adrenal Medulla:* Produces: Epinephrine (Adrenaline) and Norepinephrine (Noradrenaline): These are "fight-or-flight" hormones that increase heart rate, blood pressure, and blood glucose levels in response to stress.

Pancreas: Located near the stomach. Has both endocrine and exocrine functions. The endocrine part consists of the Islets of Langerhans, which produce: Insulin: Lowers blood glucose levels by promoting glucose uptake by cells and storage as glycogen in the liver and muscles. Diabetes mellitus (Type 1 and Type 2) is a condition where the body either doesn't produce enough insulin or cannot effectively use the insulin it produces, leading to high blood sugar levels. This can lead to serious complications like blindness, kidney failure, and nerve damage. South Africa has a high prevalence of diabetes, especially Type 2, linked to lifestyle factors.

Glucagon: Raises blood glucose levels by stimulating the breakdown of glycogen in the liver.

Ovaries (in females): Produce: Estrogen: Promotes development of female secondary sexual characteristics, regulates the menstrual cycle, and supports pregnancy.

Progesterone: Prepares the uterus for implantation and maintains pregnancy.

Testes (in males): Produce: Testosterone: Promotes development of male secondary sexual characteristics and stimulates sperm production. 2.

2. Mechanism of Hormone Action: Hormones exert their effects by binding to specific receptors on target cells. There are two main types of hormone action: Steroid Hormones (e.g., estrogen, testosterone, cortisol): These are lipid-soluble and can diffuse directly across the cell membrane. They bind to intracellular receptors (located in the cytoplasm or nucleus). The hormone-receptor complex then binds to DNA, affecting gene transcription and protein synthesis.