Endocrine and Respiratory Systems Overview

The endocrine system acts as a secondary control system in the body (after the nervous system). It's crucial for things like reproduction, regulating metabolism, and orchestrating the immune response.

Hormones are chemical messengers produced by endocrine glands. They travel through the bloodstream and act on specific target cells.

Hormones can be categorized into amino acid-based (proteins, peptides, amines), steroids (derived from cholesterol), and prostaglandins (lipid-based and act locally).

Hormones can alter cell membranes, activate or deactivate enzymes, influence cell division and secretion, and regulate gene transcription.

In direct gene activation, steroid and thyroid hormones bind to receptors inside the cell. This complex then enters the nucleus and influences DNA transcription, altering gene expression.

Some hormones, like protein hormones, bind to receptors on the cell surface. This initiates a signaling cascade involving second messengers, which amplify the signal inside the cell.

Hormones can be released due to hormonal stimuli (activation by other hormones), humoral stimuli (changes in blood composition), and neural stimuli (nervous system signals).

The pituitary gland is located at the base of the brain, connected to the hypothalamus.

The anterior pituitary produces important hormones, including growth hormone, prolactin, and tropic hormones (TSH, ACTH, FSH, LH) that regulate other endocrine glands.

The posterior pituitary releases oxytocin (involved in uterine contractions and milk release) and ADH (regulates water balance).

The thyroid hormone plays a crucial role in metabolism, regulating energy use and growth and development.

Calcitonin, produced by the thyroid, helps lower blood calcium levels, acting as a counterbalance to parathyroid hormone.

The four parathyroid glands are small structures embedded in the back of the thyroid gland.

Parathyroid hormone (PTH) is the main regulator of calcium in the blood. It increases blood calcium levels.

The adrenal glands sit atop the kidneys. The outer cortex produces corticosteroids (mineralocorticoids, glucocorticoids, and sex hormones), while the inner medulla releases catecholamines (epinephrine and norepinephrine) for the stress response.

Aldosterone, a mineralocorticoid, is produced in the adrenal cortex. It regulates water and electrolyte balance, primarily by controlling sodium reabsorption in the kidneys.

Glucocorticoids, like cortisol, are produced in the adrenal cortex. They regulate glucose metabolism, have anti-inflammatory properties, and help the body cope with stress.

The adrenal medulla releases catecholamines, primarily epinephrine (adrenaline) and norepinephrine (noradrenaline). These hormones prepare the body for "fight-or-flight" response to short-term stress.

The pancreas is both an exocrine and endocrine gland. It produces insulin and glucagon, which regulate blood glucose levels.

Insulin is released by the pancreas when blood glucose levels are high. It helps cells absorb glucose, reducing blood sugar levels.

Glucagon is released by the pancreas when blood glucose levels are low. It stimulates the liver to release stored glucose, increasing blood sugar levels.

The pineal gland produces melatonin, a hormone that helps regulate sleep-wake cycles and circadian rhythms.

The gonads (ovaries in females and testes in males) produce sex hormones. The ovaries produce estrogen and progesterone, while the testes produce testosterone.

The anterior pituitary produces six hormones: growth hormone, prolactin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyroid-stimulating hormone (TSH), and adrenocorticotropic hormone (ACTH).

The thymus gland produces thymosin, which is essential for the maturation of immune cells.

The placenta acts as a temporary endocrine gland during pregnancy, producing hormones that maintain pregnancy and support lactation.

The respiratory system's main functions are to supply the body with oxygen and dispose of carbon dioxide.

The upper respiratory tract includes the nose, pharynx (throat), and larynx (voice box). These structures filter, warm, and moisten incoming air, and the larynx is involved in speech production.

The lower respiratory tract includes the trachea, bronchi, and lungs. This is where gas exchange occurs.

Pulmonary ventilation, or breathing, is the movement of air into and out of the lungs. This is driven by pressure changes in the chest cavity.

External respiration is the exchange of gases between the alveoli (air sacs) in the lungs and the blood. Oxygen enters the blood, and carbon dioxide leaves the blood.

Respiratory capacity can be influenced by factors like age, sex, size, and overall physical condition.

Inspiration, or inhalation, involves the contraction of the diaphragm and external intercostal muscles. This expands the chest cavity, reducing pressure and drawing air into the lungs.

Expiration, or exhalation, is usually a passive process. The elastic recoil of the lungs and chest wall increases the pressure in the chest cavity, forcing air outwards. Forced expiration involves additional muscle action.

The respiratory membrane is a thin, permeable barrier that separates the air in the alveoli from the blood in the capillaries. It consists of the alveolar epithelium, the basement membrane of the alveoli, the basement membrane of the capillary, and the capillary endothelium.

Bronchial sounds are produced by air moving through large airways like the trachea and bronchi, while vesicular sounds are softer and reflect air filling the alveoli.

Oxygen binds to hemoglobin in red blood cells, forming oxyhemoglobin, for transport throughout the body.

Carbon dioxide is transported in the blood in three ways: as bicarbonate ions, dissolved in plasma, or bound to hemoglobin.

Common respiratory disorders include chronic obstructive pulmonary disease (COPD - a group of lung diseases that block airflow and make it hard to breathe), lung cancer, asthma, and pneumonia.