Digestive System Overview

Digestive System

• The digestive system consists of the digestive tract (also called the gastrointestinal tract or alimentary canal) and associated organs
• It includes the oral cavity, pharynx, esophagus, stomach, small intestine, large intestine (and anus), and organs like salivary glands, liver, and pancreas
• The main functions of the digestive system include ingestion of food, digestion of food, absorption of nutrients, and elimination of wastes

Functions of Digestive System

• Ingestion of food
• Digestion of food
• Absorption of nutrients
• Elimination of wastes

Digestive System: Structure and Components

• Serous membrane covering organs: Visceral peritoneum
• Membrane lining abdominal cavity wall: Parietal peritoneum
• Connective tissue holding organs in place: Mesenteries
• Food passage: From oral cavity to anal canal
• Components include:
  • Oral cavity (mouth)
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine: ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anal canal.
• Associated Organs:
  • Salivary glands
  • Liver
  • Pancreas

Oral Cavity (Mouth)

• Contains structures like the lips, buccinator muscles, orbicularis oris muscles, gingiva (gums), teeth, tongue, hard palate, soft palate, uvula, and tonsils

• Teeth: Permanent/Secondary Teeth; Deciduous/Primary Teeth (Milk Teeth)/Baby Teeth

• Tongue: Muscular organ with papillae (2/3 of tongue has papillae).

• Frenulum: Anterior attachment to the floor of the mouth

• Mastication: Chewing

Salivary Glands

• Parotid glands: Located beside the ear and are primarily serous.
• Submandibular glands: Located below the mandible and produce mostly serous secretions but contain mucous components.
• Sublingual glands: Smallest of the three, mainly secrete mucous saliva and located under the mucous membrane of the floor of the mouth.

Saliva

• Composition: Serous and mucous fluids.
• Functions: Moistens oral cavity, keeps teeth strong, contains enzymes to begin digestion (amylase, which breaks down food molecules, digests starches, and creates the sweet taste of food), neutralizes bacterial acids

Question: Why do babies salivate excessively or drool?

• Poor muscle development, and teething.

Swallowing (Deglutition)

• A three-step process:
  • Step 1: Tongue blocks the oral cavity, and soft palate blocks the nasal cavity
  • Step 2: The upper esophageal sphincter (UES) closes, and the tongue blocks the oral cavity
  • Step 3: The epiglottis blocks the larynx, the UES opens, and the bolus enters the esophagus; the UES closes

Egestion vs. Excretion

• Egestion: Removal of undigested material from the digestive tract.
• Excretion: Removal of metabolic wastes from the body (not just food waste).

5 Essential Nutrients

• Food provides body growth and energy.
• Includes protein, fats, and carbohydrates

Bolus & Chyme

• The bolus is liquefied in the stomach, becoming chyme.

Chyme Conversion

• Chyme mixes with bile (from liver), pancreatic juices, and intestinal juices to form chyle

Stomach

• Structure: Fundus, body, pylorus, lesser curvature, greater curvature, rugae
• Secretions: Hydrochloric acid, pepsin, mucus
• Hydrochloric acid: Kills microorganisms, activates pepsin.
• Pepsin: Breaks down covalent bonds of proteins.
• Mucus: Lubricates and protects.
• Mixing waves: Mix ingested food with stomach to form chyme
• Peristaltic waves: Force chyme towards pyloric sphincter

Small Intestine

• Parts include duodenum, jejunum, and ileum
• Absorbs most nutrients, including amino acids and fatty acids.

Large Intestine

• Parts include cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anal canal
• Absorbs water and certain electrolytes

The Colon

• • Receives Chyme from the small intestine, digesting into firm stool.*
• • Reabsorbs water and electrolytes*
• • Temporarily stores and transports feces*
• Balances electrolytes and pH

Respiratory System

• Functions include respiration (breathing), regulation of blood pH, olfaction (smell), and innate immunity.

Upper Respiratory Tract

• Components include external nose, nasal cavity, pharynx, and larynx

Lower Respiratory Tract

• Components include trachea, bronchi, and lungs

Nose (External Nose and Nasal Cavity)

• Hylaine cartilage, bone, connective tissues, & skin
• Nostrils (Nares): External openings
• Choanae: Openings to the pharynx
• Nasal Septum: Divides into left and right sides
• Hard Palate: Floor of nasal cavity, soft palate, uvula
• Olfactory Region: Receptor cells for sense of smell

Choanae (Internal Nares)

• Located at the back of the nasal cavity.

Conchae (Turbinates)

• Bony ridges in the nasal cavity that increase surface area for warming and humidifying air.

Paranasal Sinuses

• Air-filled spaces within bones, such as maxillary, frontal, ethmoidal, and sphenoidal sinuses.

Nasolacrimal Ducts

• Ducts that carry tears into the nasal cavity.

Pharynx (Throat)

• Common passageway for respiratory and digestive systems. Includes nasal cavity, oral cavity, oropharynx, laryngopharynx, and hypopharynx

Anatomy of the Pharynx

• Nasopharynx, oropharynx, and laryngopharynx are parts of the pharynx

Tonsils

• Pharyngeal (adenoid), palatine, lingual tonsils

Larynx (Voice Box)

• Composed of 9 cartilages connected by muscles and ligaments(3 unpaired: thyroid cartilage, cricoid cartilage, epiglottis; 6 paired: cuneiform cartilage, corniculate cartilage, arytenoid cartilage)

Trachea (Windpipe)

• Membranous tube of connective tissue and smooth muscle attaching to the larynx, and C-shaped hyaline cartilage. It's in the mediastinum and divides into left and right primary bronchi at the 5th thoracic vertebra. The esophagus lies posterior to the trachea.

Bronchi

• Divides into right and left main bronchi (primary bronchi) connecting to the lungs, with the left main bronchus being more horizontal.
• Right main bronchus is wider, shorter, and more vertical.
• Lobar bronchi (secondary bronchi) lead to lobes of the lungs (two on the left and three on the right)
• Segmental bronchi (tertiary bronchi) lead to the bronchopulmonary segments

Lungs and Lung Lobes

• Lungs have lobes, with the right lung having three lobes (superior, middle, inferior) and the left lung having two lobes (superior and inferior).

Alveoli

• Tiny air sacs at the end of the respiratory bronchioles in the lungs
• Sites for gas exchange (oxygen and carbon dioxide).

Inhalation Process

• Breathing in
• Air enters via the nose or mouth
• Travels down the pharynx and larynx
• Enters the trachea
• Passes through the bronchi and bronchioles
• Finally enters the alveoli
• Further filtration is done before absorption of oxygen
• Oxygen diffuses from the alveoli into blood capillaries

Gas Exchange

• Exchange of oxygen and carbon dioxide between the alveoli and blood

Movement of Oxygen and Carbon Dioxide

• Transport of gases through the respiratory system.

Breathing Phases

• Inspiration: Diaphragm and intercostal muscles contract, expanding the chest cavity and increasing lung volume. Diaphragm moves downward and blood flow in SVC increases.
• Expiration: Diaphragm and intercostal muscles relax, chest cavity contracts, and lung volume decreases. Diaphragm moves upward and returns to dome shape.

Urinary System

• Functions: controlling body fluid composition and volume, excretion, regulating blood volume and pressure, concentrating substances in blood, regulating extracellular fluid pH, regulating RBC synthesis, regulating Vitamin D synthesis

Components of Urinary System

• Kidneys, ureters, urinary bladder, and urethra

Kidneys

• Bean-shaped organs lying on the posterior abdominal wall, behind the peritoneum. One kidney is on each side of the vertebral column.
• A renal capsule (connective tissue) surrounds each kidney.
• The hilum (a medial indentation) is where blood vessels, nerves, and the ureter enter and exit.
• Divided into outer cortex and inner medulla, with renal pyramids extending toward the center.
• Urine formation processes: filtration, tubular reabsorption, and tubular secretion. Urine is mostly water and contains organic waste products and excess ions.

Blood Through Kidneys

• Blood flows through the kidneys to remove substances (excess water, ions, metabolic wastes, and toxic substances) and form urine.

Urine Flow

• Urine travels from the kidneys through the ureters to the urinary bladder, where it's temporarily stored and then eliminated through the urethra.

Renal Pelvis

• Formed by the joining of calyces, which funnel urine from the renal pyramids
• Then narrows to become the ureter
• An exit for urine from the kidneys

Nephron

• The functional unit of the kidney
• Includes renal corpuscle, proximal convoluted tubule, loop of Henle (descending and ascending limbs), and distal convoluted tubule, and collecting duct.

Renal Corpuscle

• Bowman's capsule and glomerulus
• Filtration site, where blood filters into the capsule
• The portion of the plasma entering the nephron is now a filtrate
• Bowman's capsule surrounds the glomerulus
• The glomerulus is a tuft of capillaries

Tubular Secretion

• Transports solutes across nephron walls into the filtrate

Renal Blood Flow

Team

• Team members (President, CEO, COO, VP Marketing, etc.)