Endocrine System PDF

# Endocrine System ## 7MED ACADEMY **Presented by Nidhi Sharma** **Part-1** ## Introduction - The endocrine system is a group of glands that secrete hormones directly into the circulatory system. - These secreted hormones are carried in blood towards distant target organs. ## Learning objectives...

# Endocrine System ## 7MED ACADEMY **Presented by Nidhi Sharma** **Part-1** ## Introduction - The endocrine system is a group of glands that secrete hormones directly into the circulatory system. - These secreted hormones are carried in blood towards distant target organs. ## Learning objectives This topic is divided into three parts, Part-1 will help you to: - List the glands of the endocrine system - Understand about hormones, receptors and different types of cell-cell communication - Understand the functions of the endocrine system - Understand the structure, functions and diseases of the pituitary gland - Understand the structure and functions of the hypothalamus ## Endocrine System The endocrine system consists of the following glands: - Pineal gland - Hypothalamus - Pituitary gland - Thyroid and parathyroid glands - Thymus - 2 Adrenal Glands - Pancreas - 2 Testicles - 2 Ovaries ## Hormones Now let us study about hormones - Hormones are chemical molecules in the endocrine system. - They are produced by the endocrine glands and released into the blood. - Most of the hormones are transported to different areas in the body via the circulatory system. - These hormones then regulate the functions of the target cells in specific organs. - Target cell is a cell that has the receptor for the hormone and thus binds the hormone. ## Hormone receptors Now let us study about hormone receptors. - The binding of the hormone to its receptor is described by the lock and key mechanism. - In this mechanism, a hormone binds to a receptor only if it perfectly fits in the receptor - There are two types of receptors, these are steroid hormone and Non-steroid hormone receptors. - Steroid hormone receptors are located inside the cell. Steroid hormones are steroids that act as hormones. These are derived from cholesterol. - Non-steroid hormone receptors are located on the cell surface. ## Cell-cell communication Before studying about the different endocrine glands, let us study the different types of cell-cell communication. Types of cell-cell communication include: - Autocrine communication - Direct communication - Paracrine communication - Endocrine communication ## Autocrine Communication - In this, the signaling cell and target cell is the same. - The same cell produces the hormone and binds to it. ## Direct communication - In this, the signaling cell and target cell are adjacent to each other. - Exchange of ions and hormones takes place across gap junctions. Gap junctions are connections between the plasma membrane of adjacent cells. - It occurs between two cells of the same type. - It is highly specialized and relatively rare. ## Paracrine Communication - In this, chemical signals are used to transfer information from one cell to another cell within the same issue. - This is the most common form of intercellular (between cells) communication. ## Endocrine communication - In this, hormones are released into the circulatory system from endocrine cells. - These hormones act on multiple organs and regulate their metabolic activities. ## Functions of the endocrine system. Functions of the endocrine system include: - Growth and development - Reproduction - Maintenance of homeostasis ## Pituitary gland Now let us study about the structure, functions and diseases of the pituitary gland. - Pituitary gland is a small marble-sized gland which is located at the base of the brain. - Due to its position under the brain, its called hypophysis which means "lying under". - It is attached to the brain by a stalk or infundibulum. - It is controlled by the hypothalamus and regulates the functioning of other glands such as thyroid, adrenal gland and gonads. Therefore, it's called the middle man. - As it regulates other glands, it is also called the master gland of the body. - Pituitary gland is divided into the anterior and posterior lobes. ## Anterior pituitary - It is also known as adenohypophysis. Adeno means glandular. - It is the front portion of the pituitary gland. - Anterior pituitary has three parts. These are, pars distalis, pars intermedia and pars tuberalis. ## Hormones - **Thyroid-stimulating hormone (TSH)** - It acts on the thyroid gland and stimulates secretion of thyroid or thyroxine hormones. - **Prolactin (PRL)** - It stimulates production of milk by the breasts in women who are pregnant or have just given birth. It also helps in development of breasts. - **Follicle-stimulating hormone (FSH)** - It helps with the regulation of menstrual cycle and production of eggs by the ovaries. In men, it helps with the production and maturation of sperms by the testicles. - **Luteinizing hormone (LH)** - It stimulates the ovaries and testicles to produce oestrogen and testosterone respectively. ## Normal hormone levels - **Adrenocorticotropic hormone:** - Males: 7-50 pg/ml - Females: 5-27 pg/ml - **Growth hormone:** - Males: <5 ng/ml - Females: <10 ng/ml - **Thyroid-stimulating hormone:** 0.4-5 miu/l (milli-international units per litre) - **Prolactin:** - Males: 2-18 ng/ml - Females: 2-29 ng/ml - **Follicle-stimulating hormone:** - Males: 1.3-19.3 miu/l - Females: - 3.1-7.9 miu/l (follicular phase) - 2.3-18.5 miu/l (ovulation peek) - 1.4-5.5 miu/l (luteal phase) - **Luteinizing hormone:** - Males: 3.1-34.0 IU/I - Females: - 1.9-12.5 IU/I (follicular phase) - 8.7-76.3 IU/I (peek of menstrual cycle) - 0.5-16.9 IU/I (luteal phase) ## Posterior pituitary - Posterior pituitary is also known as pars nervosa or neurohypophysis. - It contains the extensions of the neurons present in the hypothalamus. - It is the back portion of the pituitary gland. ## Hormones - The hormones secreted by the posterior pituitary are produced by the hypothalamus. They include: - **Antidiuretic hormone (ADH)** - It regulates re-absorption of water in the kidneys. Normal range: 1-5 pg/ml - **Oxytocin** - It stimulates labor contractions during child birth and helps in milk ejection during breastfeeding. ## Disorders - **Growth hormone deficiency:** it is also known as growth hormone hyposecretion and is caused due to pituitary growth failure. It leads to dwarfism which means abnormally low stature or small size of an individual. It also leads to retarded growth, abnormal fat distribution and low blood glucose levels hours after a meal. - **Growth hormone overproduction:** it is also known as growth hormone hypersecretion. It causes gigantism and acromegaly. In both these conditions, there is excessive growth. Due to the excessive secretion of growth hormone, hands, feet and face grow abnormally large. - **Thyroid-stimulating hormone deficiency** - It causes hyperthyroidism or an overactive thyroid gland. This leads to overproduction of thyroxine hormone by the thyroid gland. - **Thyroid-stimulating hormone overproduction** - It causes hypothyroidism or an underactive thyroid gland. Due to this, the thyroid gland is unable to produce enough thyroxine hormone. - **Prolactin overproduction** - It is also known as hyperprolactinaemia. It is caused due to the formation of a tumor on the anterior pituitary which leads to secretion of large amounts of prolactin. - **Antidiuretic hormone deficiency** - It leads to a rare condition, known as diabetes insipidus. In this, due to hyposecretion of ADH, the kidneys do not reabsorb water from urine. This leads to dehydration, thirst and polyuria. Polyuria is excessive production and excretion of urine. - **Antidiuretic hormone overproduction** - It leads to syndrome of inappropriate antidiuretic hormone secretion (SIADH). In this, due to hypersecretion of ADH, the kidneys do not excrete water optimally. This leads to water retention and increased water content/body mass. ## Hypothalamus Now, let us study about the structure and functions of the hypothalamus. - It is located on the undersurface of the brain. - It lies above the pituitary gland. - It is attached to the pituitary gland by the stalk or infundibulum. - It contains the nerve endings of many neurosecretory cells. - Neurosecretory cells are cells that convert neural signals into chemical signals. - It helps in maintaining homeostasis. - It responds to changes in body temperature, hunger, feeling of being full, blood pressure and hormonal levels in the circulation. - It also responds to stress and controls our body’s circadian rhythm. For example, night-time secretion of melatonin from the pineal gland. - Hypothalamus controls the release of hormones from the anterior pituitary lobe by producing inhibiting hormones (IH) and releasing hormones (RH). - The rate of secretions of these hormones is controlled by a negative feedback mechanism. An example of this is given in the figure. In this, hypothalamus secretes a releasing hormone which stimulates the release of hormone 1 from the anterior pituitary. Hormone 1 acts on an endocrine gland and stimulates it to release hormone 2 which then acts on its target cells. When the concentration of hormone 2 increases beyond its normal limit, it will send the signal to the hypothalamus to stop secretion of the releasing hormone. This is known as negative feedback. ## Releasing hormones (RH) These hormones stimulate the secretion of hormones from the anterior pituitary lobe. Examples of releasing hormones and their downstream targets are given in the table. | Releasing Hormones (RH) | Hormone 1 (from anterior pituitary)| Hormone 2 (from target organ) | Endocrine target organ | |---|---|---|---| | Thyrotropin-releasing hormone (TRH) | TSH | Thyroxine hormones | Thyroid gland | | Corticotropin-releasing hormones (CRH) | ACTH | Glucocorticoids | Adrenal cortex | | Gonadotropin-releasing hormone (GnRH) | LH | Inhibin | Testicles | | | | Inhibin and Oestrogen | Ovaries | | | FSH | Testosterone | Testicles | | | | Progesterone and Oestrogen| Ovaries | ## Inhibiting hormones (IH) These hormones prevent the secretion of hormones from the anterior pituitary lobe. For example, prolactin-inhibiting hormone inhibits the secretion of prolactin from the anterior pituitary lobe. ## Time for the quiz ### Quiz-1 Q. Which of the following is not a function of the endocrine system? A. Respiration B. Growth and development C. Reproduction D. Maintenance of homeostasis ### Quiz-2 Q. The signaling and target cell is the same cell in which type of cell-cell communication? A. Endocrine B. Paracrine C. Autocrine D. None of the above ### Quiz-3 Q. Which of the following glands is not an endocrine gland? A. Thymus B. Pancreas C. Hypothalamus D. None of the above ### Quiz-4 Q. What is the normal range of growth hormone in females? A. 12 ng/ml B. 15 ng/ml C. >5 ng/ml D. <10 ng/ml ### Quiz-5 Q. Thyrotropin-releasing hormone stimulates the secretion of which hormone? A. Oxytocin B. Thyroid stimulating hormone C. Follicle stimulating hormone D. Prolactin ## Answer to the quiz 1. A 2. C 3. D 4. D 5. B ## Summary You have completed the topic *The Endocrine System* - Part-1. | Topic Section | Content | |---|---| | ORGANS | Glands of the endocrine system | | CELL-CELL COMMUNICATION | Hormones, receptors and cell-cell communication | | FUNCTIONS | Functions of the endocrine system | | PITUITARY GLAND | Structure, functions and diseases of the pituitary gland | | HYPOTHALAMUS | Structure and functions of the hypothalamus | ## References - Anatomy and physiology in Health and illness - Ross and Wilson.