hormones and the digestive system (1)

Overview of Circulation and Gas Exchange

• Title: Chapter 42 Circulation and Gas Exchange

• Authors: Nicole Tunbridge and Kathleen Fitzpatrick

• Source: Pearson Education, Inc. © 2017

• This chapter covers important concepts from previous chapters regarding the endocrine system (Chapter 40) and the human digestive system (Chapter 41) as they relate to circulation and gas exchange in the body.

Hormones and the Endocrine System

• Function of Hormones: Hormones are chemical signals released into the circulatory system, facilitating communication and regulatory messages throughout the body. Although hormones circulate throughout the body, they exert effects only on target cells that contain specific receptors for them.

• Endocrine vs. Nervous System: The endocrine system is responsible for slower, long-lasting regulatory functions, encompassing reproduction, development, energy metabolism, growth, and behavior. In contrast, the nervous system quickly relays information via electrical signals through specialized cells, neurons.

Intercellular Communication

• Types of Signaling: Signaling between animal cells is categorized based on the type of secreting cell and the signal's pathway to the target cell. The main forms include:

  • Endocrine Signaling: Hormones released into the bloodstream promote homeostasis and mediate physiological responses.

  • Paracrine Signaling: Local regulators influence nearby target cells by diffusion.

  • Autocrine Signaling: The secreting cell also acts as the target.

  • Synaptic Signaling: Neurons communicate with target cells via neurotransmitters at synapses.

  • Neuroendocrine Signaling: Neurosecretory cells release neurohormones to enter the bloodstream.

Endocrine Tissues and Hormones

• Endocrine Glands: Ductless organs that secrete hormones directly into the surrounding fluid. Main endocrine glands include:

  • Hypothalamus

  • Pineal gland

  • Pituitary gland

  • Thyroid and parathyroid glands

  • Adrenal glands

  • Pancreas

  • Gonads (ovaries and testes)

• Hormone Classes: Hormones can be categorized based on their solubility:

  • Water-soluble hormones (e.g., peptides and some amines) cannot easily cross cell membranes and bind to surface receptors.

  • Lipid-soluble hormones (e.g., steroid hormones) easily diffuse through cell membranes and may interact with intracellular receptors.

Mechanism of Hormone Action

• Cellular Response: Water-soluble hormones initiate a signal transduction pathway upon binding to cell-surface receptors, leading to a series of responses, including enzyme activation or changes in gene expression. Lipid-soluble hormones enter target cells and typically influence gene regulation directly.

Local Regulators

• Local regulators facilitate communication among nearby cells and can influence the secreting cells themselves. Examples include:

  • Cytokines and growth factors

  • Nitric oxide (NO)

  • Prostaglandins (involved in inflammation and pain response)

Nutrition and Digestive System Overview

• Animal Nutrition: Incorporates processes such as ingestion, digestion, absorption, and elimination, critical for acquiring energy, organic building blocks, and essential nutrients.

• Classes of Animals Based on Diet: Animals are typically categorized into three groups: herbivores (plant eaters), carnivores (meat eaters), and omnivores (both plants and animals).

Essential Nutrients

• Nutrients necessary for growth and health must be acquired through diet. These include:

  • Essential Amino Acids: Required amino acids that humans cannot synthesize and must obtain from foods.

  • Essential Fatty Acids: Necessary unsaturated fats that must be consumed.

  • Vitamins: Organic substances required in small amounts, categorized into fat-soluble and water-soluble groups.

  • Minerals: Inorganic elements necessary for various bodily functions, also needed in smaller quantities.

Digestive Process

• The human digestive system is composed of a complete digestive tract. Key structures include:

  • Oral cavity

  • Pharynx

  • Esophagus

  • Stomach

  • Small Intestine

  • Large Intestine

• Digestion in the Stomach: The stomach stores food and secretes gastric juice, which digests food into a liquid called chyme. The acidic environment (pH 2) helps in protein denaturation and bacterial destruction.

• Small Intestine Digestion: Most enzymatic hydrolysis occurs here, with the pancreas supplying enzymes and the liver producing bile that aids in fat digestion.

• Absorption in the Small Intestine: Characterized by a large surface area due to villi and microvilli; nutrient absorption is facilitated through both passive and active transport mechanisms.

• Large Intestine’s Role: Responsible for water recovery and the formation of feces, accommodating mutualistic bacteria that contribute vitamins and support epithelial development.

Homeostasis and Feedback Mechanisms

• Regulation of Digestion and Appetite: Hormones play crucial roles in regulating digestion, energy storage, and appetite through feedback loops involving various body systems.

• Diabetes Mellitus: A condition resulting from imbalances in insulin and glucagon levels, affecting glucose homeostasis.