---
# System prepended metadata

title: Digestive System
tags: [Y2, Science]

---

- consists **alimentary canal** (hole) and organs associated with it

# Stages of Nutrition
- Ingestion -> mouth
- Digestion -> mouth, stomach, small intestines
- Absorption -> Small & Large intestines
- Assimilation -> liver, body cells
- Egestion -> Rectum, Anus
	- Ejection of undigested matter

## Ingestion
- Food enters body through the. **mouth**, which leads into the **buccal cavity** (mouth area)
- Digestion of food begins in the mouth by the teeth, salivary glands and tongue

## Buccal cavity
- Chewing action of teeth breaks up larger pieces of food into smaller pieces
- The tongue rolls the food into small, slippery, round masses or **boli**
- Saliva **softens** food and contains **salivary amylase** that digests **starch to maltose**
- The salivary glands in the mouth secrete saliva, **pH 7**, which is **mixed by the tongue**

### Physical Digestion
- Teeth
	- Chewing breaks down food into smaller pieces
	- increase **surface area to volume ratio** for chemical digestion
- Tongue
	- **Mixes** food with saliva and **rolls** food into small round masses called **bolus**
- Saliva
	- **Moistens** food for easier swallowing and rolling

### Swallowing*
- The food bolus passes from the mouth to the **pharynx** and into the **oesophagus**
- Flap called **epiglottis** covers the **windpipe**, preventing the food from entering it
## Oesophagus
- muscular tube
- channels food to the stomach
- Walls are made of 2 layers:
	- Longitudinal (outer) muscles
	- Circular (inner) muscles
	- Muscles fibres are circular
		- In ring shape
- Food moves down the oesophagus via peristalsis
- Very little chemical digestion takes place
- Peristalsis aids in physical digestion of food

## Peristalsis
- rhythmic, wave-like muscular contractions
- in the wall of the alimentary canal
- longitudinal muscles and circular muscles are antagonistic
	- When one contracts, the other will relax
	- e.g. biceps and triceps

|                       | Circular muscles        | Longitudinal muscles     |
| --------------------- | ----------------------- | ------------------------ |
| Benind the bolus      | Contract (Tube narrows) | Relax (Tube lengthens)   |
| In front of the bolus | Relax (Tube widens)     | Contract (Tube shortens) | 

![](https://hackmd.io/_uploads/HkU-YBqih.jpg)

- helps food move along the gut
- Enables food to be mixed with digestive juices

## Stomach
- muscular organ lined with folds and ridges on the internal surface
- Entrance and exit controlled by two sphincter muscles
- 2 pH cuz $\ce{HCl}$
- Physical digestion:
	- Churning action in stomach
- Chemical digestion:
	- Gastric juice excreted by 
- Contains HCL, mucus and the protease
- HCL optimum pH for action of protease and kills harmful microorganisms in food
- protease in gastric juice catalyse the break down of proteins into polypeptides
- takes 2-3 h to convert bolus to chyme
- Why not digest itself:
	- Mucus lining secrete alkaline bicarbonate, that neutralises the acid pH

### Stomach ulcers
- meals not eaten regularly
- gastric juice will digest stomach lining if not mixed with food
- Gastric meds contain bases and carbonates

### Stomach surgeries
- Adjustable gastric band procedure
- Roux-en-Y Gastric Bypass
	- Reduce fat digestion

## Small Intestine
- Food passes from stomach to small intestine
- consists of the duodenum, jejunum and ileum
- 7m long in an adult
- Bulk of chemical digestion occurs in first part

### Associated organs
- Liver:
	- produces bile liquid
- Gall bladder:
	- stores bile before releasing
	- bile released from bile duct
- Pancreas:
	- secretes pancreatic juice
	- produce lipase

### Action of Bile
- bile salts **breaks up** large fat globules into small fat droplets
- increases SA:V ratio
- emulsification
- **NOT A CATALYST!!! ONLY INCREASES SA:V RATIO!!!!** 
	- Cuz no chemical change
	- Only physical digestion

### Digestion in Small Intestine
- intestinal juice, pancreatic juice and bile secreted into the small intestine
- all alkaline, helps neutralise the acidic chyme
- pancreatic juice contains pancreatic amylase, pancreatic lipase and pancreatic protease (tripsin)
	- works on **larger molecules**
- intestinal juice secretes:
	- maltase
	- sucrase
	- lactase
	- intestinal protease
	- intestinal lipase
	- works on **smaller molecules**
Carbohydrate digestion:

| Source                                         | Enzyme  | Mode of action                 |
| ---------------------------------------------- | ------- | ------------------------------ |
| Pancreas                                       | Amylase | Starch -> Maltose              |
| Glands on epithelial lining of small intestine | Sucrase | Sucrose -> Glucose + Fructose  |
| Glands on epithelial lining of small intestine | Maltase | Maltose -> Glucose             |
| Glands on epithelial lining of small intestine | Lactase | Lactose -> Glucose + Galactose |

Protein digestion:

| Source     | Enzyme   | Mode of action             |
| ---------- | -------- | -------------------------- |
| Pancreas   | Protease | Protein -> Polypeptide     |
| Intestinal | Protease | Polypeptide -> Amino Acids | 

Fat digestion:

| Source     | Enzyme | Mode of action                 |
| ---------- | ------ | ------------------------------ |
| Pancreas   | Lipase | Glycerol + 3 Fatty Acid Chains |
| Intestinal | Lipase | Glycerol + 3 Fatty Acid Chains |

### Absorption
- Long channel increase time for absorption
- **folds**, **villi** and **microvilli** increase SA:V, highly branched
- Villi:
	- **One cell layer of microvilli** to separate from blood
	- short diffusion distance
- Adaptations:
	- Digested food substances transported away from the **blood capillaries** and **lacteals** to maintain concentration gradient for **diffusion**
- **Glucose** and **amino acids** absorbed into **blood capillaries** by **diffusion** or **active transport**
- **Water**, **mineral salts** & **vitamins** are also absorbed
- **SMALL INTESTINE RESPONSIBLE FOR MOST WATER ABSORPTION**
- Fats:
	- **glycerol** and **fatty acids** diffuse into epithelial cells
	- recombine to form fats
	- packaged into special **lipoprotein** structure

![](https://hackmd.io/_uploads/HyCJLB5j2.jpg)

Overview:

![](https://hackmd.io/_uploads/BJ8J8rqin.jpg)


## Large Intestine
- consists of the colon and the rectum
- about 1.5m long
- appendix is useless
- Undigested food moves along the gut, solidifies and turns into faeces
- Absorbs water, mineral salts and vitamins
- Faeces stored in rectum before being expelled

## Diabetes
- Medical condition in which blood glucose levels remain **persistently higher** than normal
- Type 1 diabities
- Type 2 diabetes
- Gestational diabetes

| Type 1                                           | Type 2                                                              |
| ------------------------------------------------ | ------------------------------------------------------------------- |
| Cannot be prevented                              | Can be prevented via lifestlye modifications                        |
| Body does not create enough insulin              | Body does not create enough insulin develops insulin resistance     |
| Causes are unknown, but genetics may play a role | Causes include family history, aging, inactivity, obesity, and more |
| Requires insulin injections for life             | Requires insulin as needed, injected or oral                        |

Similarities:
- Can cause serious health problems
- Requires healthy lifestyle and medical supervision
- Symptoms includes thirst, frequent urination, and blurry vision

Risk factors for Type 2 Diabetes:
- unhealthy diet
- overweiht
- physical inactivity
- old age

# Overview
![](https://hackmd.io/_uploads/HksAHBcsh.jpg)


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